BRITISH FOSSILS. 



Decade III. Plate IV. 



HEMICIDARIS INTERMEDIA. 



[Genus HEMICIDAEIS. Agassiz. (Sub-kingdom Eadiata. Class Echinodermata, 

 Order Echinidse. Family Cidarites.) Body sub-globose ; interambulacral segments very 

 broad, bearing (few) primary perforated tubercles placed on crenated mammillary eleva- 

 tions ; ambulacral areas very narrow, furnished with primary tubercles on their lower 

 portions ; pores in single file, except close to the mouth, where they are ranged in threes ; 

 summit crowned with a disk composed of five ovarian and five ocular plates surrounding 

 a central anus ; spines of two orders, the primaries long, cylindrical, mostly of considerable 

 dimensions, the secondaries small, compressed.] 



Diagnosis. H. testa subglohosd, areis ambulacralibus infra tuber culis 

 majoribus confertis, inter ainbulacralibus tuberculis approximatis ; spinis 

 subteretibus, cylindricis, longitudinaliter striatis, striis minutis, basi tumido. 



Synonyms. Variation of Cidaris papillata, Parkinson, Organic Re- 

 mains, vol. iii., p. 14, pi. 1, fig". 6; and pi. 4, fig. 20. Cidaris intermedia, 

 Fleming, Brit. Animals, p. 478 (1828). Hemicidaris crenularis, Morris, 

 Cat. of Brit. Fossils, p. 53 (1843). — Buckman and Strickland's Edition of 

 Murchison's Geology of Cheltenham, pi. 13 (1845). 



The most common example of the genus Hemicidaris in British 

 collections, is the species before us ; the abundance and perfection of 

 specimens rendering it a favourite fossil. It is usually regarded as the 

 Cidaris crenularis of Lamarck, and is cited under that name in memoirs 

 and works on English geology. For the following reasons, however, I 

 feel obliged to reject the appellation of crenularis as applied to the 

 English species, and to omit the usual citations and references to 

 Lamarck and older authors, and to Goldfuss, Desmoulins, Agassiz, and 

 Desor. 



In the "Description des Echinodermes Fossiles de la Suisse," 

 Agassiz has described at length and figured the Hemicidaris crenularis 

 of Switzerland as the species of Lamarck and other authors. He has 

 presented a specimen in remarkably perfect condition, its spines being 

 entire. The figures are excellent, but the species, as the spines plainly 

 show, is not the so-called crenularis of British geologists. As the 

 bodies of the two species can only be critically distinguished from each 

 other — unfortunately a frequent case in this genus — it is difficult to 

 know to which the figures of Goldfuss, and the imperfect older repre-" 



[ill. iv.] B 



