174 SYNOPSIS OF THE CHARACTERS OF THE 



EcHiNOCKiNUS URii. Flem. sp. (PL XXVII. fig. 1). 



Echinus, lire's Hist. Ruth. — Cidaris Urii. Flem. Brit. Anim. — Cidaris Benburbiensis. Portk. Geol. Rep. 



Sp. C/i.— Spines with tlieir lower third finely striated longitudinally ; upper two-thirds ' with about five 

 or six longitudinal, alternating rows of short, strong spines. Plates having the central perfijratcd tubercle sur- 

 rounded by a single ring ; margin with rounded radiating ridges. 



Tliis species difi^rs from the C Urii of Fleming, in having but one ring round, the tubercles, and having 

 the margins of the plates radiatingly ridged instead of granulated ; both of these characters depend so much on the 

 preservation of the specimen, that their presence or absence may in some measure be considered as accidental, a 

 very slight disintegration causing the ridges to assume the appearance of tubercles ; so that the present species is 

 very probably the same as that of Fleming, the spines agreeing perfectly. Spines of this species frequently at- 

 tain to three and a half inches in length ; cyhndrical, slightly broader in the middle of the min-lcated part ; 

 diameter at base two lines, length of plate figured seven lines, breadth four lines. 



ECHINOCRINUS VETUSTUS. Phil. SP. 

 Cidaris vetusta. Phil. Geol. York. 



It is very possible that the spines referred to this species may really belong to the upper part oi E. Urii, 

 being rather smaller but muricated in the same manner ; the murication extends nearer to the base in the pre- 

 sent species. 



Adelocrinus HISTRIX. PJtil. 

 Adelocrimas histrix. Phil. Pal. Fos. 

 A single specimen of this curious fossil has occured ; like Professor Phillips's specimen, it was a cast in soft 

 shale ; the specimen was about one inch in diameter, and half an inch long, conical, undivided, and covered 

 with scattered, spine-like tubercles. The specimen was imperfect at each end, and irregularly crushed, so that 

 I am unable to add any information to that already known, or even to say whether it truly belong to the Cri- 

 noidea. It seems very closely allied to the Echinus Humboldtii of Steininger. 



Pentremites. Sat/. 



Gen. C/i. — Pelvis of three unequal plates, two pentagonal, and one tetragonal, supporting five large sca- 

 pula ; ambulacra five, column round ; surface of articulation radiated. 



Pentremites Derbiensis. Sow. 



Pentremites Derbiensis. Sow. Zool. Journal Pentremites Derbiensis. Phil. Geol. York. 



Sp. Ch. — Spheroidal; length slightly exceeding the width ; pelvis concave; sutures about one-third the 

 length from the base ; surface granulated. 



This beautiful little species is easily distinguished from any of those described by Mr. Gilbertson, by its 

 small size, and nearly basal sutures. Length four lines. 



Pentremites ellipticus. Sou: 



Pentremites ellipticus. Sow. Zool. Juur. 



Sp. Ch. — -Longitudinally ovate, length one-third greater than the width ; base truncate, concave ; sutures 

 mesial ; surface obscurely striated and granulated. 



This species, in its lengthened, elliptical form, resembles the F. uhlunrjus, but is at once distinguished by 

 its mesial sutures. 



