214 PALAEONTOLOGY OF NEW-YORK. 



e\-idence. It is also possible that what appears to be a minute single semicircular plate, on the 

 upper excavated edge of the costal plate, may be composed of three smaller plates. These 

 parts are very minute, and almost always much obscured or dilapidated, and I have given 

 therefore only what has been actually seen. Until recently, this fossil has been one of the 

 most rare species ; but some fortunate discoveries have shown, that in certain thin layers, it 

 ' is quite numerous, having no great vertical range, and probably restricted in its geographical 



extent. It is extremely rare to find specimens with the coronal processes still attached entire ; 

 and it is only by carefully separating those found imbedded in shale, that they are obtained 

 in perfection. 



Fig. 1 a. A specimen of the ordinary form and proportions, having a part of the column attached. 



Fig. 1 J. A specimen more elongated, and somewhat flattened. 



Fig. 1 c. A small specimen with very prominent carina;. 



Fig. I d. A similar larger specimen, with the body somewhat rotund and the carinaj very strong. 

 The coronal processes are broken off, in this and the preceding specimen. 



Fig. 1 £. Three of the costal plates arranged laterally, showing the single and two converging 

 . carinas, and the succeeding coronal plates. 



[ Fig. 1 /. The lefthand side of one of the heptagonal pelvic plates, above which the costal plates 



divide, showing one of the carina3 extending from the base obliquely to the summit. 



Fig. 1 g. The base of a specimen, showing the three divisions, and the depression for the attach, 

 ment of the column. 



Fig. 1 h. Figure showing the form and arrangement of plates of the body. 



Fig. 1 i. The crown, as it usually appears when destitute of the plates, diverging from and 

 I supporting the central proboscis. 



I Fig. 1 !i. The crown, preserving the plates as described above. 



Fig. 1 I. An enlarged figure, showing the structure and arrangement of the plates forming the 

 summit. F is the summit of the costal plates, slightly bent inward, and sustaining 

 the succeeding small plate, from which two narrow elongated plates proceed to the 

 central proboscis. H, the plates holding the place of scapulars, and forming the elon- 

 gated coronal plates, which, on their inner truncated angles, support the five plates 

 of the proboscis. On the lower plate of this series, as the figure is arranged, and 

 near its inner angle, is the small elevation composed of five minute plates, and sur- 

 rounding an aperture opening into the cavity below. 



Fig. 1 m. A transverse section at the base of the costal plates, showing the subdivisions of the 

 plates, and the projecting angles of the carinse. 



Position ami locality. In the Niagara shale at Lockport. The specimens, usually destitute 

 of a column and of the coronal processes, are often found at the base of the cliff, washed out 

 by rains from the decomposing shale. (Statt Collection.) 



