File:Bulletin - New York State Museum (1901) (19821124643).jpg

Title: Bulletin - New York State Museum
Identifier: bulletinnewyork491901newy (find matches)
Year: 1887 (1880s)
Authors: New York State Museum; New York State Museum
Subjects: Science
Publisher: Albany : New York State Education Dept
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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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 tapering to a broad margin of larger and smaller plates. In others the rays are all solar, as in A. alleganius, 1 Cln. soc. nat. hist. Jour. 1887. 10:25.

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