Species ofPentremites. 317 



used are so vague, that I have not been able to ascertain the fact, 

 I think nevertheless, that " Pelvis deep saucer-shaped, convex," 

 may serve to distinguish it from both. I shall now proceed io 

 describe, as well as I can, the two species of this interesting 

 Genus that I have met with. 



SpECits 4. Pentremites Derbiensis. Subglobosa, superne, latior; 

 granulosa. Pelvis minimus, pentagonalis, concavus ; scapii- 

 lares mediocres, subdepressEe, superne latiores, emargina- 

 tionis interscapularis angulo obtusissimo ; interscapulares 

 maximi, ad centrum superne fere attingentes ; ambulacra 

 lineares, angusti, prominentes, series duas confertas moni- 

 lium efFormantes. Long. ■^■^. Lat. f unc. 



In general form the Pentremites Derbiensis may be described 

 as subglobose, its upper extremity being rather broader ; its 

 pelvis is very small, pentagonal, and concave, according, how- 

 ever, most strictly with the generic character ; scapulars middling 

 in size, pressed down and the interscapular notch at the upper 

 edge having a very obtuse angle ; these are much shorter than in 

 the succeeding species and much wider at the upper part than at 

 the base : interscapulars very large, reaching nearly to the center 

 at the upper extremity, and about three-fifths of the distance from 

 the upper towards the lower, broad at their base : ambulacroi 

 linear, narrow, rather prominent, formed as it were by the lateral 

 union of two strings of little beads. The whole surface of the 

 pelvis, scapulars and interscapulars is covered with minute grains, 

 and both on the scapulars and interscapulars there are horizontal 

 striae, which may probably be the lines of growth. 



Two specimens of this curious fossil were sent some years ago, 

 by Mr. White Watson, to my late father, in whose collection 

 they now remain : by Mr. Watson they were called Echini, he 

 supposes them to be peculiar to Derbyshire, and states that they 

 belong to the twenty-sixth bed of limestone. 



Species 5. Pentremites elliptica : elliptica, infra subtruncata ; 

 pelvis minimus, pentagonalis, subconcavus ; scapulares max- 

 imi, superne latiores, emarginationis insterscapularis angulo 



