128 CYPHOSOMA 



Genus — Cyphosoma, Agassiz, 1840. 



Cyphosoma, Agassiz, 1840. 

 Phymosoma, Haime, 1853. 

 — Desor, 1858. 



Cyphosoma, Cotteau, 1863. 



Test moderate in size, circular or subpentagonal, slightly inflated at the sides. 

 Poriferous zones well developed and undulated, composed of simple pores that in 

 general are unigeminal throughout, and sometimes are bigeminal on the upper surface, 

 and crowded a little together around the peristome. The poriferous plates are un- 

 equal and irregular in their mode of arrangement. The primary tubercles are nearly 

 equal in size in both areas, the areolae are well developed, and sometimes marked with 

 radiated striations ; the bosses are prominent, and have their summits sharply crenu- 

 lated ; the mammillon is large, prominent, and imperforate, and the general facies of the 

 test shows a regular, and uniform development of all its several elements. The mouth- 

 opening is large, the peristome slightly incised, and the oral lobes nearly equal. The 

 discal opening is large and pentagonal, one angle of which extended far into the single 

 inter-ambulacrum ; the elements of the disc were feebly united, as they are absent in all 

 the specimens that have hitherto been collected. 



The spines are long, solid, subcylindrical, aciculate, or spatuliform ; sometimes they 

 are straight and lanceolate, or bent, ramiform, or spoon-shaped ; all these varieties are 

 figured in Pis. XXIV and XXVI. The stem is smooth and marked with fine longi- 

 tudinal striae, the milled ring is prominent, the head distinct, and the rim of the aceta- 

 bulum crenulated. 



The genus Cyphosoma is distinguished from all others by its prominent tubercles 

 with crenulated bosses, and imperforate mammillons ; in the structure of these it resembles 

 lEicMnocyphus and Tenmopleurus, but is readily distinguished from these by the absence of 

 the angular and sutural impressions which impart so mai'ked a character to their tests. 



M. Desor has separated into the genus Coptosonia all those Cyphosomata from the 

 Nummulitic formation (Tertiary) with much undulated poriferous zones, tubercles with 

 very large mammillons, and having the plate-sutures of the areas deeply incised ; thus 

 leaving the typical Cyphosomata as true Cretaceous fossils, which first appear in the 

 Neocomian beds, and attain their maximum development in the upper stage of the 

 White Chalk. 



The Cretaceous rocks of Prance are very rich in species of Cyphosoma, of which a 

 very small proportion have hitherto been found in the British islands. 



