L. Agassiz on the Echinodermata. 301 



rr 



anterior ambulacrum formed of minute equal pores ; the lateral am- 

 bulacra formed each of two series of double pores, differing among 

 themselves, the posterior series being much more marked than the 

 anterior. One species, from the chalk. 

 H. radiatus, Ag. (Spatangus rad., Lam.) 



5. Micraster (Spatangus, auct. ; Brissoides, Klein. ; Amygdala 

 and Ovum, V. Ph.). — Dorsal portion of the ambulacra highly deve- 

 loped and rather starlike ; disc heart-shaped. The most part of the 

 species are fossils from the chalk ; there are some tertiary, and two 

 living. 



M. Amygdala, Ag. (Spat. Amygd., Gold/.) — M. Bucklandii, Ag. (Spat. 

 Buck]., Goldf.) — M. Bucardium, Ag. (Spat. Bucard., Gold/.) — M. Bufo, 

 Ag. (Spat. Bufo, Al. Br.)—M. Cor. anguinum, Ag. (Spat. Cor. Aug., Law.} 

 — M. Cor. testudinarium, Ag. (Spat. Cor. test., Goldf.) — M. gibbus, Ag. 

 (Spat, gib., Lam.) — M. Goldf usii, Ag. (Spat, lacun., Goldf, non Gmel.) — 

 M. Prunella, Ag. (Spat. Prim., Lam.) — M. acuminatus, Ag. (Spat, acum., 

 Goldf) — M. suborbicularis , Ag. (Spat, subovb., Munst.) — M. canaUferus, Ag. 

 (Spat, canal., Lam.) — M. lacunosus, Ag. (Spat, lacun., Gmei, non Goldf.) 



6. Spatangus, Klein and Gray. (Echinospatangus , Breyn.) — Disc 

 heart-shaped ; with a large, deep, anterior dorsal groove ; the ambu- 

 lacra of this groove are formed of minute equal pores, which, near the 

 summit and at the circumference, present the form of a star. Be- 

 sides the small spines, which are smooth on the back, there are some 

 larger ones, but very slender. There are some fossil species from the 

 chalk and tertiary deposits, and several living species. 



Sp. ornatus, Al. Br. — Sp. Desmarestii } Munst. — Sp. Hoffmanni, Goldf. — 

 Sp. purpureas, Leske. — Sp. meridionalis, Riss. — Sp. ovatus, Leske. — Sp. 

 Crux Andrea, Lam. — Sp. planulatus, Lam. 



7. Amphidetus, Ag. (Echinocardium, V. Ph. and Gr. — Spatan- 

 gus, De Blainv., Sect. A.) — Disc heart-shaped, anterior dorsal groove 

 deep, in which lies the odd ambulacrum, which is formed of minute 

 pores, and is prolongated between the anterior ambulacra. The se- 

 ries of double pores which form the four ambulacral pairs are at a 

 distance from each other towards the summit of the disc, and gra- 

 dually approximate towards the periphery in the form of a star. The 

 spines are very remarkable, the larger being arched and spatuliform 

 at their extremity, the others are small and smooth. I know but of 

 one fossil species from the chalk, and two living. 



A. Gold fusii, Ag. (Spat, arcuarius, Goldf, non Lam.) — A. Sebce, Ag. 

 (Echinocardium Sebse, Gr.) — A. pusillus, Ag. (Spat, pusillus, Leske.) 



8. Brissus, Kl. and Gr. (Eclii/iobrissus, Breyn. — Nuces, V. Ph. 

 — Spatangus, De Blainv., Sect. D.) — No anterior dorsal groove ; odd 



