220 PALAEONTOLOGY OF NEW YORK. 



cretion retains two plates in juxtaposition, one of which indicates that the true 

 form was sub-conical, appressed at the sides, with a broadly rounded, somewhat 

 flattened dorsum. The anterior margins, from the apex to the base, appear to 

 have been distant, leaving a broad cleft between them. Some of these charac- 

 ters are also shown upon the flattened specimens. There is but one exception 

 exhibited to the general sub-triangular form of these plates, and that is afforded 

 by a small example in which the apex is central and both anterior and poste- 

 rior margins convex. The substance of the valves is chitinous, tenuous and 

 reduced to a carbonaceous film; the surface is ornamented by concentric undu- 

 lating ridges, which are closely crowded near the apex, and also near the basal 

 margin in old specimens. The dorsum shows traces also of fine, elevated 

 radiating lines. 



These plates vary in size from a length of 6 mm. and a height of 5 mm. to 

 a length of 27 nun. and a height of 20 mm. Fragments also indicate a very 

 much greater size. 



Observations. The fossils which constitute this species vary widely in some 

 features from those referred to Plumulites by M. Barrande, as well as from other 

 species of this genus occurring in the rocks of New York State. All these 

 are of very much smaller size, and are simple plates, never folded or rounded 

 over the back or conical, and are usually characterized by a conspicuous ridge 

 passing from the apex to near the basal margin. It is difficult to see how the 

 combination of these sub-conical bodies in vertical ranges could produce such a 

 scaly peduncle or capitulum as existed in Turrilepas. Should the anterior mar- 

 gins of these valves prove to be cleft from apex to base, they will resemble 

 much more closely in form, contour and surface sculpture, the fossils which 

 have been described under the genus Spathiocaris (page 199). 



Distribution. In the black shales at Sheffield and Birmingham, Erie county, 

 Ohio. In Mr. Whitfield's description the fossils were referred to the "Huron 

 shale," equivalent to the Genesee shales and the lower portion of the Portage 

 shales of New York ; Dr. J. S. Newberry has however, in corrected labels upon 

 the specimens, referred them to the "Cleveland shale," the uppermost Devon- 

 ian strata of Ohio. 



