202 PEOr. p. M. DUNCAlSl'S llEVISION OP THE 



whicli stould be placed after tlie genus, for there is no evidence 

 that Lamarck wrote upon it. The genus first appeared in the 

 -Catal. rais., Ann. des Sci. Nat. vol. vii. p. 168 (1847). Agassiz 

 there wrote : — " The genus links the Cassidulidse and the Spa- 

 tangoids ; it has the shape of AnancMtes, but differs from it in the 

 mouth, which is median and pentagonal. The ambulacra are 

 united together at the summit, and the odd one has the pairs of 

 pores smaller and more distant than in the paired petals, almost 

 }ike the Spatangoids. At the actinal surface the ambulacra 

 correspond to broad and deep grooves. Anus posterior." The 

 apex is evidently excentric in front. Agassiz defined the genus 

 to include Clypeaster excentricus, Lam. 



The next notice of the genus is in d'Orbigny's description of 

 the Echinodermata, Pal. Frang., Terr. Cret. vol. vi. 1853-55, 

 p. 279, pis. 906, 907, 908. 



Genus Asteeostoma, Agassiz, 1847, Ann. d. Sci. Nat. vol. vii. 

 p. 168. Cotteau, 1871-73, Mem. /Soc. Geol. de France, ser. 2, 

 vol. ix. ii. p. 178. 



The peristome is subpentagonal, not labiate, central or slightly 

 in front. There are five actinal grooves from the peristome 

 reaching the margin of the test, corresponding with the ambu- 

 lacra. Anus posterior, marginal. 



Ambulacra broad, subpetaloid, unequal ; odd ambulacrum 

 flush, with very small pores, circular and in simple series in 

 regular pairs. Paired ambulacra flush, long, not contractiug 

 near the ambitus ; pores simple, large, equal. Tubercles distant, 

 scarce. 



Fossil. Cretaceous ? : Cuba. 



The species is Asterostoma excentricum. Lam. sp., a very large 

 form, 103 millim. long. It will be observed that the test is oval, 

 longer than broad, broadest in front and slightly narrows be- 

 hind ; convex above, rounded in front, less so behind, tumid at 

 the ambitus, flat actinally, with five grooves ; ambulacra above 

 the ambitus subpetaloid. In the plate 906. fig. 1 there is no 

 anterior groove above the margin, and certainly the radial ends 

 of the ambulacra are not sufficiently distant to enable any one to 

 infer that the apical system was elongate. The species was 

 probably FcMnolampas Kleinii. There is no doubling of the 

 pairs of pores at the peristome, and there is no sternum to the 

 posterior interradium. On plate 908 the antero-lateral ambu- 



