NIAGABA GEOTTP. 



215 



600. 2. STEPHANOCRINUS GEMlVnFORMIS (n. jp.)- 



Pl. XLVIII. Fig. 2o-t. 



Column round, composed of joints of equal thickness ; canal round, minute, articulating 

 surfaces of joints minutely crenulated or denticulated near tl^ outer margin ; body triangular 

 at base, rapidly enlarging above, and becoming rotund in the middle and slightly contracted 

 near the summit ; structure as in the preceding ; pelvic plates three, short, angular below, and 

 becoming curved above ; costal plates five, succeeded by an equal number of plates forming 

 the spiniform processes around the summit ; upper margins of the costal plates scarcely de- 

 pressed or excavated ; structure of the summit precisely as in the preceding species ; surface 

 granular. 



This species is usually minute, the largest entire specimen seen being figured in 2 a, b. It 

 is clearly distinct from the preceding, not only in size and form, but in surface markings. The 

 plates have no carinse upon their surfaces ; and though the form is more sharply triangular at the 

 base, it nevertheless expands rapidly, and becomes rotund above. At the base of the third 

 range of plates, the fossil is slightly contracted ; which contrasts strongly with the preceding 

 species, which has its greatest breadth at this point. The coronal processes are slightly con- 

 verging, while in the other they are diverging. There is otherwise no appreciable difference in 

 the structure. In one or two specimens, the structure of the crown has been distinctly observed. 

 In all its parts there is the most perfect similarity of structure, with slight differences in the 

 proportions. 



A single fragment has been found, where the base indicates that the entire individual was 

 twice or thrice as large as the largest one figured. 



Fig. 2 a. An individual somewhat larger than the ordinary size. The position in which it is 

 figured, shows the pentagonal pelvic plate, and the short sloping sides of the ad- 

 joining plates. 



Fig. 2 J. A specimen wilh a few joints of the column attached. 



Fig. 2 c. The crown of an individual, as it is usually seen. 



Fig. 2 d, e. The base of one of these, and the same enlarged, showing the rapidly expanding 

 form which becomes nearly round or very obtusely pentagonal at the centre. 



Fig. 2 /. The structure of this species as shown from fig. 2 a. 



^ 'g- 2 g'. A small specimen, where the base is much drawn out, and quite triangular. 



Fig. 2 k. The same enlarged, showing more distinctly the form and proportions. 



Fig. 2 i. A portion of the surface enlarged, showing the character of the ornament. 



Position and locality. In the shale at Lockport. Usually found at the base of the cliff, 

 washed out by the rains. ^siate Collection.) 



