FOSSILS OF THE KKOKTK (iKOUP. 507 



or about three times as long as wide, and gradually taper- 

 ing upward ; all extremely prominent along the middle, and 

 sloping strongly inwards laterally, very sharply carinate 

 below the pseudo-ainbulaeral areas. Summit openings very 

 small and closely approximated. Interradials very small, 

 or only about one-tenth as long as the radials. Pseudo- 

 ambuluiTal areas remarkably narrow or sublinear, and 

 deeply sunken, extending down rather more than half the 

 entire length of the body, or about two-thirds the length 

 of the radial pieces; pore pieces minute, slightly oblique, 

 and numbering about one hundred to each side of each area, 

 the two rows of each area being separated by a deep mesial 

 furrow, along Avhich the inner ends of the pore pieces are 

 minutely crenate: lanceolate and supplementary pore pieces 

 unknown. Surface marked with microscopic lines, as fine, 

 ivii'iilar and crowded as if made by an engravers ruling 

 machine. 



Hight. 2.25 inches; breadth. 1.64 inches; breadth of base, 

 1.14 inches; hight of do., 0.50 inch; depth of excavations 

 along the sutures of base, 0.20 inch; breadth of do., from 

 0.45 to 0.56 inch; length of pseudo-ambulacra! areas, 1.45 

 inch; breadth of do., 0.08 inch. 



This extraordinary form differs so widely from all other known species, 

 as to render a comparison of its specific characters with any of those 

 hitherto described entirely unnecessary. It seems to be related to a 

 group of species characterized by a triangular base, and very narrow 

 pseudo-ambulacra! areas, for which Dr. SHOIARD has proposed tne 

 name Ti-oo*to<-riHu*. Still it presents some rather strongly marked dif- 

 ferences from that group, the species of which have the body narrow, 

 fusiform, and more or less elongate and tapering below, with the tri- 

 angular base merely flattened on each of the three sides. In our type, 

 however, the body is broadest below, while the base is coinparatively 

 very short and wide, and has the three spaces corresponding to the 

 flattened sides of the typical species of Troostocrinm so very profoundly 

 and broadly excavated, as to impart a very remarkable appearance to 

 the lower part of the fossil. Should it be thought desirable to desig- 

 nate this type by a distinct subgeneric name, it might be called J/ 

 locrinm, in allusion to the three deep excavations of the base. 



