GENERA AKD GEOUPS OP THE ECHIKOIDEA. 181 



d'Orb. He observes (Eevision, p. 342) that Lamarck's genus 

 contained two types, G. lapis-cancri and C. carihhearwn, with 

 C. Marmini, the former being retained to represent the typical 

 Cassidulids, and the others being associated with the genus 

 Bhynchopygti.s by Desor and Liitken. He places, however, this 

 last-mentioned genus as a subgenus. I consider that tliis is 

 the correct view, and therefore the most beautiful and elaborate 

 drawings of G. carihlearum and other forms given by Loven, in 

 his Etudes, figs. 61-67 & 130, 179, relate to the subgenus. 

 Desor relied too much upon the taxonomic value of one of the 

 structures of Gassidulus, viz. the cribriform or smooth tubercle- 

 less median actinal band, which has been sliown by Loven to be 

 unimportant, as it may be seen in the subgenus as well as in 

 the type ; or it may not exist (see also A, Agassiz, Eevision, 

 pi. XV. fig. 3). The only distinction is the lateral extension of 

 the overhanging periproct of Bhynchopygus. 



Grenus Cassidulus, Lamarck, 1801, Syst.Anim. sans Vert. p. 348. 

 Agassiz Sf Desor, 1847, Cat. rais., Ann. Sci. Nat. vii. p. 157. 

 Desor, 1858, Synopsis, p. 288. LutJcen, 1863 (pub. 1864), 

 Vid. Medd.f. Naturh. Foren. i Kj'obenh. p. 126. A. Agassiz, 

 1872-74, Eevision, p. 342. 



Syn. TrocJialia, Pomel, 1883= Asterobrissus, De Loriol, 1888. 



Test small, oblong, depressed, broadest posteriorly, longer 

 than broad, broader than bigb, convex abactinally, flat actinally. 



Apical system excentric in front or subceutral ; four perforated 

 basal plates ; the madreporite passing back and separating the 

 postero-lateral basals, but not the radial plates. 



Ambulacra subsimilar, short, flush, subpetaloid, not closing ; 

 pores continued from the petaloid part to the floscelle, which is 

 well developed. Tentacles both simple and branchial (hetero- 

 podous). 



Peristome excentric in front, the bourrelets narrow and strong, 

 the pbyllodes in grooves. One peristomial plate to each inter- 

 radium. Usually a median band behind the peristome where 

 there are no tubercles, and where the test is either cribriform, 

 pitted, or plain, or it may be absent. The periproct supramar- 

 giual, at tbe commencement of a groove, elongate longitudinally. 

 Tubercles small and very close abactinally, large and distant 

 actinally, except on the median area posteriorly. 



