On some New Features in <i>Pelanechinus corallinus</i> .

Abstract

In vol. xxxiv. p. 924, of the ‘Quarterly Journal of the Geological Society,’ Mr. Walter Keeping, F.G.S., described two specimens of a form previously referred by Dr. Wright to the genus Hemipedina . He showed that this form was quite distinct from Hemipedina , and gave it the name of Pelanechinus . It showed, in his opinion, affinities with the Echinothuridæ on the one hand and the Diadematidæ on the other. These two specimens have hitherto been the only ones known, with the exception of a few fragments described by Dr. Wright. I was fortunate enough to find in 1881 in the Coral Rag at Calne, in a quarry at the north end of the town, a third specimen which shows some interesting features hitherto undescribed. The diameter of the test is about 85 millim.; it is considerably flattened from above downwards. The whole of the oral surface is beautifully preserved, with the exception of a sector including one ambulacral and the greater part of two interambulacral areas. The teeth are exposed in situ , together with most of the peristomial imbricating plates; the latter, however, are not exhibited so clearly as in the specimen in the Woodwardian Museum. A zone, about 15 millim. wide, belonging to the oral surface is also preserved. My specimen quite confirms Mr. Keeping's opinion that the test was flexible. The plates have frequently separated along the line of suture, especially on the aboral surface, while the median interambulaeral line and the lines of junction between the ambulacral and