298 CYSTOIDEA, BLASTOIDEA, AND HOLOTHUROIDEA. 



its mode of attachment. Salter regard's the genus as refer- 

 able to the Sponges. 



Cycloerinus, again (fig. 176, e), has a globular body, also 

 covered with hexagonal or pentagonal plates, the apex being 



Pig. 176. a, Pasceolus Halli, of the natural size (after Billings) ; 6, Pasceolus globosus, of 

 the natural size (after Billings) ; c, Sphcerospongia melliflua, of the natural size (after Salter) ; 

 d, Four of the integumentary plates of the same, enlarged ; e, Cycloerinus Spaskii, of the 

 natural size (after Ferd. Roemer) ; /, Part of a vertical section of the same ; g, Part of the 

 last, showing the structure of the integument, enlarged ; h, Part of the mould of the inner 

 surface, enlarged ; i, Diagram of a vertical section of Nidulites favus, showing the form 

 of the body and integumentary plates, and the supposed peduncle (original). All the 

 specimens are from the Silurian. 



provided with an aperture and the opposite extremity with 

 a small peduncle. The plates themselves are cup-like, of 

 considerable thickness (fig. 176, /and g) t with an inward 

 central projection which leaves a median pit in casts of the 

 interior (fig. 176, h). 



Lastly, in Nidulites (fig. 176, i) we have ovate, globular, 

 or pyriform, hollow bodies, which were probably attached 

 by a pedicle, and which have an integument composed of 



