The ollgolamellar, flat type of echinoid teeth in Kongielechinus magnituberculatus gen.n., sp.n. is described. The teeth consist of few relatively large, thick, roughly triangular lamellae. Re-interpretation of the teeth structure of the oldest known echinolds - Upper Ordovician Aulechinus and Ectinechinus is presented. It is suggested that their teeth also belong to the flat, oligolamellar type and have been hitherto wrongly assigned to the grooved type. A new lepidocentrid Kongtetechtnus magnitubercutatus gen.n., sp.n. from the Givetian (Middle Devonian) of Poland is described on the basis of isolated coronal plates, spines and Aristotle lantern elements.
Plesiechinus hawkinsi n. sp. from the Middle Lias of Nevada, U. S. A., the oldest and most primitive representative of an irregular echinoid family of the Pygasteridae Lambert, 1900, displays a "regular" apical system with genital 5 perforate. Crenulate tubercles in the new species contest earlier opinions on the derivation of pygasterids from echinoids with smooth tubercles.
The author presents the results of an analysis of the test in Pygomalus ovalis , P. analis , Pygorhytis ringens, Collyrites sp. and Disaster n. sp , where she has observed the presence of the 5th genital plate. Its displacement is discussed and is shown to be similar to that occurring in the ontogenetic development of Echinocardium cordatum. Moreover, in order to homologize the plates of the apical system in echinoids, the writer has also used the crystallographic method, on the ground that the optic axis of the particular plates displays a fairly constant inclination angle. It is supposed that in some genital plates the in clination angle of the optic axis is determined by its position in the remains of the larval skeleton around which these plates arise.
Le présent travail contient les résultats des études des Échinides irréguliers du Dogger de Pologne, appartenant à trois familles: Galeropygidae Lambert, Echinobrissidae d'Orbigny et Disasteridae Gras, représentées dans les matériaux par 11 espèces, dont deux sont nouvelles, et 3 sous-espèces (deux nouvelles). L'analyse détaillée de la morphologie a révélé la persistance, chez les représentants primitifs de ces familles, du type de l'appareil apical qui ne diffère en rien, en ce qui concerne les traits essentiels, de l'apex des Échinides réguliers. Le matériel disponible a permis aussi de suivre les étapes successives de l'évolution de l' appareil apical vers le type irrégulier. Ce processus est identique dans les trois familles, mais diffère de celui que l'on observe par exemple chez Pygaster. Les parties adorales des ambulacres (phyllodes) des familles examinées accusent l'identité de leur structure et évolution. L'étude sur la différenciation de l'interambulacre impair chez les Disasteridae a fourni l'objet de la discussion concernant l'homologie des éléments du plastron. Sur la base des résultats obtenus l'auteur présente ses idées sur la parenté réciproque des familles examinées et discute la valeur des structures décrites pour le problème de l'origine de la famille des Disasteridae et de ses descendants. Dans les remarques finales l'attention est attirée sur les points communs dan s la morphologie des Échinides examinés d'une part, et de la famille des Acrosalenidae de l'autre, ce qui fait penser à la parenté possible de ces deux groupes d'Échinides.
Oligolamellar echinoid teeth, primitive in general morphology, are represented in the Givetian of the Skały beds (Grzegorzowice-Skały Section, Holy Cross Mts, Poland) by a few types differing mainly in fine details of their adaxial surfaces which may be smooth, ledged or denticulate. It is suggested that these characters reflect the adaptation to particular feeding habits. A new kind of Givetian echinoid teeth, closely related to the oligolamellar one is described. In some characters such as greater number of lamellae which also are thinner, they seem to be “intermediate” between oligolamellar and another group of Givetian echinoid teeth, for which the name multilamellar is proposed. It is newly recognized and briefly characterized.
Considered as holectypoid (Gnathostomata) Pygaster microstoma Lambert, 1933 from the Toarcian of Morocco is actually the most primitive galeropygid (Atelostomata) for which the new genus Eogaleropygus is proposed. Incipient “irregular” position of the periproct and very shallow anal groove are in sharp contrast with much more advanced evolutionary changes such as small size and unnotched peristome (external manifestations of the loss of dental apparatus and gills) as well as dense and unordered tuberculation. The morphology of Eogaleropygus suggests that galeropygids became atelostomate probably long before they became bilateral.
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