30(5 L. Agassiz on the Echinodermata* 



spines arc often tubular, The tubercles of tlie ambulacral plates, 

 although equally perforated, are smaller and more numerous than in 

 Cidaris. There arc fossil speeies from the jura and chalk, and 

 many recent. 



D. Beeheif Ag. (Cid. Bech., Broiler.) — D.subangulare, Ag. (Cidarit. sub- 

 ang., Gohlf.) — 1). vagantf Ag. (Cidaris vag., Phil.) — I), mammillanuni, 

 Ag. (Cidarit. mam., Ilivm.) — D. Lemispliaricum, Ag. (Jura.) — 1). trans- 

 trr.su m, Ag. (Jura.) — D. variolar e, Ag. (Cidarit. variol., Al. Br.) — D. gra- 

 n/ilusum, Ag. (Cidarit. granul., (I old/.) — D. ornatum, Ag. (Cidarit. orn., 

 Gold/.) — D. rotularc, Ag. — D. setosum, Gr. — D. calamarium, Gr. — D. spi- 

 nosissimum, Ag. (Cidarit. spinos., Lam.) — D. sabularc, Ag. (Cidarit. subul., 

 Lam.) — I), pulvinatum, Ag. (Cidarit. pulvin., Lam) 



3. AsTRorYGA, Gray. {Cidarites, Lam.) — Shell flattened ; ambula- 

 cra large, and converging uniformly towards the summit; oviducal 

 plates very long, lanceolate ; several vertical series of spines on the 

 interambulacral spaces. One living species only. 



A. radiafa, Gray. 



4. Salenta, Gr. {Cidarites, auct.) — This genus resembles that of 

 Cidaris by the disposition of the ambulacral plates, but they bear a 

 large mammilla, whose summit is not perforated. Around the anus, 

 instead of small moveable laminae, there are large scutelli (ecussonsj 

 articulated at their margins. The oviducal plates are also very large. 

 All the species are fossils, from the jura, or chalk. 



5. Hoffmanni, Ag. (Cidarit. HofFm., Roem.) — S. hemispharica, Ag. (Ci- 

 darit. hemisph., Roem.) — 6". scutigera, Gr. — S. peltata, Ag. 



5. Echinometra, Breyn., V. Phels., and Gr. (Echinus, auct.) — 

 Shell oval transversely and obliquely to the longitudinal axis, more 

 or less flattened ; large tubercles on the interambulacral spaces, bear- 

 ing spines of very varied forms. Mr. Gray thought he perceived in 

 the obliquity of the ambulacra an objection to the bilateral arrange- 

 ment which I had observed in the Echinodermata ; but this is merely 

 one example more of the want of symmetry notwithstanding the 

 similarity of the parts, as is found in most Mollusca. M. Wieg- 

 mann, in return, has very well observed, that their longitudinal dia- 

 meter is shorter than the transversal. The species belonging to this 

 genus are all recent. 



E. atrata, Gr. — E. acufera, De Bl. — E. carinata, De Bl. — E. Lesche- 

 naultii, De Bl. — E. lobata, De Bl. — E. Litcunter, Gr. — E. Malhcei, De Bl. — 

 E. mammillata, Gr. — E. Mangei, De Bl. — E. oblonga, De Bl. — E. pedifera, 

 De Bl. — E. Quoyii, De Bl. — E. trigonaria, De Bl. 



6. Arbacia, Gray. (Echinus, auct.) — True Echini, similar to the 

 Diadcma, but the tubercles are not perforated. Ambulacral spaces 



