On Cyclocystoides, a new geyms of Echinodermata from the Lower and 

 Middle Silurian Rocks. By J. W. Salter, Esq., of the Geolo- 

 gical Survey of Great Britain ; and E. Billings, Esq., of the 

 Canadian Geological Survey. 



Under this name we wish to describe a form which has come 

 under the notice of each of us — in the one case in a series of 

 instructive specimens shewing the structure of the different parts 

 from the Trenton limestone rocks of Canada ; and in the other, a 

 specimen shewing the entire form and general surface, which has 

 been long known in the Llandovery Rocks or May-Hill Sandstone 

 of England. 



The affinities of the fossil may perhaps be better discussed when 

 the structure of the two species with which we are acquainted has 

 been described. 



Genus Cyclocystoides, Billings and Salter. ?LAr£X. 



Generic Characters. — Discoid, surfaces formed of an integument 

 composed of numerous small granular plates, which appear to be 

 radiately arranged; margin entirely surrounded by thick subquadrate 

 plates, each of which presents upon its outer half two deep obtusely 

 oval excavations. These, in perfect specimens, are covered over by 

 minute polygonal plates, thus forming a tubular channel around the 

 whole animal. This channel appears to have been connected with 

 the interior by small pores penetrating through the marginal plates, 

 there being one pore leading from each of the excavations. The 

 margin or (perhaps) disc was also connected with a long tube, like 

 the proboscis of some of the Crinoids, formed of many small polygo- 

 nal plates. 



I. Cyclocystoides Halli, Billings. 



Description. — Flat, circular, from one to two inches in diameter; 

 about thirty-six marginal plates, the unexcavated inner portions of 

 which are subquadrate, convex, and slightly granular upon their 



