. Bulletin - New York State Museum. La science. Nouveau AGELACRINITES 189 les grandes plaques peuvent être themiselves et périphériques projet- ward au-dessous du niveau de la surface aborale (A. Un 11 e g a n i u s) ou toutes les plaques d'être marginal et uniforme de petite taille (A. c en à cinn ien tr s), avec la zone périphérique à l'extérieur du mur circulaire très large (A. A.) legrandensis buttsi, ces plaques ou être à la fois grandes et petites (A. dicksoni). Agelacrinites holbrooki James de l'Siluric supérieur a l'espaces interradial pavée avec une mosaïque de cinq et six plaques recto verso, alors que le taux marginal d'imbricating les plaques.

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. Bulletin - New York State Museum. Science. NEW AGELACRINITES 189 the larger plates may themiselves be peripheral and project down- ward below the level of the aboral surface (A. a 11 e g a n i u s) or all the marginal plates be of uniform and small size (A. c in cinn at ien si s), with the peripheral area outside the circular wall very broad (A. buttsi, A. legrandensis) or these plates be both large and small (A. dicksoni). Agelacrinites holbrooki James of the upper Siluric has the interradial spaces paved with a mosaic of five and six sided plates, while the marginal plates are imbricating.^ This condi- tion, though piponoun/ced in this spe- cies, is also apparent in less degree in all species with mosaic plates over the interradii. Smch a combination of plating would seem essentially to neutralize the influence of the char- FiG. 2 A. holbrooki James. Anal acter of the thecal plates alone as a region much enlarged, showing the ^ mosaic plates of the interradii, the generic fcature, wheu cousldered in- squamous plates of the margin, the crowding of small plates about the anal dependently Of Othcr StrUCture. It pyramid and the terminations of R 1 and 5. Between the cover plates of was the difference iu this rcspoct the latter will be observed minute . accessory plates, two for each interval, indicated by the first species above mentioned, together with a difference in the attitude of the rays, that furnished to Meek occasion for introducing his term, Lepidodiscus, for the squamous forms. Madreparite. Dr Bather has indicated the presence of a madre- pore in his copied figures of A. cincinnatiensis and A. h a m i 11 o n e n is i s {op. cit. p. 205). I have, however, seen nothing in any agelacrinite that can be safely thus designated, Rays. Direction. Of the species of "Agelacrinus", some of the early . Siluric forms like A. b i 11 i n g s i Chapman of the Trenton and A. bohemicus Barr. (Etage D), have the rays sharp and quite straight, abutting against or t

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• bookcentury1800
• bookdecade1880
• booksubjectscience
• bookyear1887