DORYDERMA. 155 



ends, and throughout covered with spinous projections, which frequently terminate 

 in minute facets. 



The examples of this genus have hitherto only been known from the Jurassic 

 strata of Germany and Switzerland, but in the Carboniferous Limestones of 

 Ireland, detached skeletal-spicules are present, which so closely resemble those of 

 the typical forms of the genus that they may provisionally be referred to it. 



37. Cnemidiastrtjm peiscdm, Hifide, sp. nov. Plate V, figs. 6, 6 a — 6/. 



1880. Lithistid (dendritically branched surface spicule), Carter. Ann. and Mag. 

 Nat. Hist., ser. 5, vol. vi, p. 212, pi. xiv b, fig. 12. 



This name is proposed for detached spicules of irregular forms, either curved, 

 or variously branching, and terminating in small twig-like extensions. Minute 

 spinous processes with facetted ends project from the surface of the spicules. 

 The spicules vary from *5 to *8 mm. in length, and from *075 to '2 mm. in 

 thickness. 



These spicules are of not infrequent occurrence in the beds of decayed Carbo- 

 niferous chert at Ben Bulben, associated with the spicules of Spiractinella and 

 other hexactinellid and lithistid Sponges. As a rule they are quite detached 

 from each other, but fragments of the skeleton occur in which two or three of the 

 spicules are united together by the apposition of their spinous processes in the 

 same manner as in the Jurassic examples of the genus. 



Distribution. — Carboniferous Limestone : Ben Bulben, near Sligo, Ireland (J. 

 Wright). 



Family. — Megamorina. 



Genus. — Doryderma, Zittel. 



1878. Studien iiber fossile Spongien. Zweite Abth. Abhandl. d. k. bayer. Akademie 

 der Wissenscbaften, CI. ii, Bd. xiii, Abth. 1, p. 131. 



Syn. — Spongia (in part), Mantell, Phillips; Spongites (in part), Mantell ; Poly- 

 jerea (in part), Roemer, Quenstedt ; Polypothecia (in part), Benett. 



Generic Characters. — Sponges either simple or compound; cylindrical, pear- 

 shaped, or dendriform, with cylindrical branches. The main body of the Sponge 

 (and also the branches when present) is traversed longitudinally by parallel tubes 



