194 Proceedings of the Royal Physical Society. 



Messrs Woodward and Barrett have likewise pointed out 

 how the form of the plate and anchor is in Syna/pta of 

 specific importance, and I think we may be justified in 

 extending this principle by placing the present plates and 

 anchors in a distinct genus. Especially may this be the 

 case, when we recollect that little or no chance exists of 

 our ever acquiring a knowledge of the complete animal. I 

 therefore propose for the remains in question the name of 

 Achistrum.'^ 



Little difference appears to exist between the wheel-plates 

 of the recent Cheirodota and those now under description, 

 and I shall content myself in this instance with simply re- 

 ferring them to this genus. 



The remaining spicules offer greater difficulties in referring 

 them to their recent analogues. The cross-like bodies have 

 some analogy with spicules from the integument of Ciicu- 

 maria Hyndmanni, Forbes (PI. VL, Fig. 9), figured by Diiben 

 and Koren,f although the resemblance is only a general one. 



Similarly, the serrated bodies previously described may be 

 compared generally with calcareous elongated bodies, having 

 an undulated or serrated margin met with in the integument 

 of C. frondosa, Linn. (PL VL, Fig. 11). Figures of these are 

 also given by Messrs Diiben and Koren. X 



Lastly, the small tooth is quite analagous to the pieces 

 composing the oesophageal ring in many genera — for instance 

 in Thyonefusus (Miiller), as figured by Koren. § 



To conclude, the following are the abbreviated characters 

 of the genus and species I propose to establish for these 

 remains of Carboniferous Holothuroidea. 



Genus Achistrum, Gen. nov. 



Gen. Char. — Plates of integument irregularly oval in form ; 

 perforations variable in number and size; articular process 

 for anchor absent. Anchor spicules in the form of a one- 

 fluked plain (?) hook. Size of plates varying from ^Q-th to gV^l^ 

 of an inch ; size of perforations, from ^^^ to ^}^ inch. 



* dyKicTTpov, a fish-hook. 



t K. Svenska Akad. Handlingar, 1844, t. 4, f. 13. t Loc. cit., t. 4, f. 1. 



§ Nyt Magazin for Naturvidenskaberne, 1845, iv., t. 4, f. 4. 



