DESCBIPTIONS or Tin; 8PECLES. 267 



lateral portions of the plates with an obliquely flattened band, limited or marked off 



by a fine hair-like ridge. Deltoid plates triangular, short, and broad, with constricted 

 apices, and the centre of each plate occupied by a flattened linear petaloid space; 

 posterior deltoid almost entirely occupied by the anus. Ambulacra elongately 

 petaloid, somewhat arched, projecting above the margins of the sinuses, and even 

 above the surface of the summit; the food-groove strongly marked; side plates 

 twenty-two. llydrospire-slits seven or eight, one being always partly concealed. 

 Mouth very distinctly pentagonal. Anus rhombic-triangular, and very large. 

 Column circular ; canal minute. Ornament of very fine stria? parallel to the 

 outline of the plates, those on the marginal bands of the radial plates being 

 particularly distinct. 



Ill marks. This species does not require comparison at all with the British G. trilo- 

 batus. So far as can be judged from the measurements of the other Carboniferous 

 form, ('. WTlitei, Hall, in the absence of a figure, the two appear to be quite distinct. 

 C. pyramidatus may be distinguished from C. Hindei by its more attenuated base, 

 convex summit, arched and prominent ambulacra, and the marginal bands on the radial 

 plates. Dr. B. F. Shumard describes the radials of C. Americanus as quite devoid of 

 these obliquely flattened portions, but we doubt whether it is anything more than 

 what he called " a strongly marked variety ;" and the same remark applies to the 

 specimen figured by Hall l as C. pyramidatus, " or a closely allied species." According 

 to Mr. C. AYachsmuth 2 the Cadaster alter nat us of Lyon 3 was founded on more than 

 one species. One of these 4 he considers to be the form afterwards described by 

 Shumard as C. pyramidatus, the present species, and would retaiu this name for it. 

 The other 5 Mr. Wachsmuth believes to represent a distinct genus, for which he has 

 proposed the name Heteroschisma, retaining Lyon's trivial name altematus for the 

 species. We are inclined to agree with Mr. Wachsmuth that the two forms are 

 distinct specifically, but we differ from him on the generic question, as already 

 pointed out G ; for we regard both the species figured by Lyon as true Codasters. 

 The second one, Cadaster altematus (PI. X. figs. 19, 20), differs from the first, 

 C. jiyrainidatus, Shum. (PL XII. figs. 1-3), in possessing a concave or inwardly 

 excavated summit, in the absence of the flattened bands around the interradial 

 sutures, and in other minor points. Mr. Wachsmuth believes that this specimen, 

 which we have figured on PL X., is a varietal form of C. altematus, which he has 

 proposed to call C. elongatus, but as it is the only example of Lyon's species which 

 we have seen we can offer no opinion upon this point. 



Localities and Horizon. Columbus, Ohio : Corniferous Limestone, Lower Devonian 



1 Fifteenth Ann. Report New York State Cab. Nat. Hist. 1S02, p. 152, pi. 1. figs. 12, 13. 

 - Report Geol. Survey Illinois, l)ss3, vol. vii. p. 354 (note). j 



3 D. D. Owen's 3rd Report Geol. Survey Kentucky, lb-37, p. 4'J3. 



i Ibid. pi. 5. £ 3,6. 5 Ibid. L 3,«. « AnUa, pp. 30-34, & 203, 204. 



2 M 2 



