BRITISH FOSSILS. 



3 



out satisfactorily in this species. The tubercles are most numerous 

 below. The spines are unknown. 



The mouth and anus are of about equal dimensions, being each in 

 diameter rather less than one-eighth of the length of the shell. The 

 position of the mouth is subcentral, but sometimes the eccentricity is 

 considerable. It is very obscurely decagonal, but seems to the eye as if 

 round. No traces of dental armature have as yet been discovered. 



Varieties. — The specimens we have figured accord best with the 

 representations of the Dysaster Eudesii of Agassiz, as figured in the 

 Monograph by Desor. Many Englisli examples are, however, suflfi- 

 ciently flattened out to represent very perfectly the ringens of that 

 work. In the description of the species there given it is implied that 

 the latter differs from the former importantly in the circumstance of its 

 anterior ambulacra being narrower than the posterior ; the figures of D. 

 Eudesii, however, represent the ambulacra as presenting similar relative 

 proportions with those of ringens. M. Cotteau refers this Dysaster of 

 the " oolite ferrugineuse" of the Tour-du-Pre to the ringens. His 

 figure would serve as a good representation of some of our English 

 specimens. He remarks that he and M. Moreau have collected in 

 a single locality a suite of examples of D. ringens presenting various 

 degrees of tumidity and more or less circularity of outline, and among 

 which were all the gradations conducting to D. Eudesii " qui ne serait 

 alors qu'une variete plus petite et plus allongee du Dysaster ringens. 

 The experience of the Survey collectors leads me to the same con- 

 clusion. 



Professor M*Coy, in his memoir On some new Mesozoic Radiata," 

 in the " Annals of Natural History" for December, 1848, has enumerated 

 D. Eudesii as a British species from the inferior oolite of Dundry and 

 Bridport. At the same time he describes two new species of Dysaster 

 under the names of D. symmetricus and D. suhringens ; the former " not 

 uncommon in the inferior oolite of Bridport," the latter "not uncommon 

 in the inferior oolite of Dundry and Leckhampton." After a careful 

 perusal of his descriptions, I am obliged to surmise that the latter 

 species (an opinion supported, after comparison with the original speci- 

 men, by Mr. Salter), is a variety of the species now described. I can 

 find no character in his descriptions which would warrant their specific 

 separation ; and, as in the case of his suhringens, he compares it with 

 ringens and Eudesii, distinguishing it from the former " by its greater 

 gibbosity and the less prominence of the ridges on the under side," and 

 from the latter " by the disproportionate narrowness of the three anterior 

 ambulacra as in the D. ringens characters which vary in every speci- 

 men, I do not hesitate to include it among the synonyms of ringens. In 

 the same paper he mentions Dysaster avellana, of Agassiz, as also from 

 the inferior oolite of Bridport ; I cannot satisfy myself, after examining 



