.1. W. GREGORY — RELATIONS OF ECHINOID FAUNAS. 107 



characters of a viviparous form, while Schizastt r scella was probably the same. The 

 occurrence therefore of these species in both the Mediterranean and Antillean 

 faunas is quite sufficient of itself to demonstrate the inadequacy of any explanation 

 based on the passage of the pluteal forms ; some of the forms that crossed the At- 

 lantic had an abbreviated development without any pluteal stage. 



The Pliocene Faunas. 



In the Pliocene period the echinoidea are scarcer and less well known than in 

 the Miocene, and now that most of the species described by Ravenel ami Tuomey 

 have been transferred to the earlier division no very definite fauna is left. In fact 

 on the mainland there are only a few recent species, such as Mellita sexforis from 

 Carolina and Echinarachnius excentrieas (syn. Scutella striatula, Rem. non Marc.de 

 Series) from the Pacific slope. The collections of the Academy of Natural Sciences 

 of Philadelphia an i the Smithsonian Institution also contain some specimens of 

 the living Echinanthus reticulatus, Linn. sp. (sensu Loven; the Echinanthus — or 

 ( 'lypeaster — rosaceus, A net.) from Coloosahatchie, Florida. These, however, seem to 

 be all recent species, whereas in the European Pliocene but few living species are 

 represented. The few echinoids from beds of this age in the United States have no 

 particular afiinities with the European ones. 



There are, however, two species of echinoidea from deposits in the West Indies 

 that may be referable to this age, and which cannot be overlooked, as they have 

 important bearing on questions of physical geography. They are ( 'ystechinus crassm, 

 Greg., ami Asterostoma, n. sp., both from the Radiolarian marls of Barbados. The 

 geological bearing of the discovery of such a typically deep-sea genus as Cystechinus 

 was referred to at the time of its description, but it has gained considerably in in- 

 terest by the recent w r ork of Profess. >r Agassiz. At the time of the discovery of the 

 Barbados specimen the genus was only known from the Antarctic and the China 

 sea. It has now, however, been dredged by Professor Agassiz in deep water off the 

 western coast of Central America, but the species is so far known only by the few 

 remarks made about it by Professor Agassiz in his preliminary report on the results 

 of the cruise ; yet as far as we can judge from these it is cl< isely allied. The species 

 of Asterostoma is of interest from the Light it throws on the age of the beds in Cuba, 

 from which the original specimens of this genus were derived, from their resem- 

 blance to Echinocorys (Ananchytes). M. Cotteau referred them to the Cretaceous, 

 but the discovery of this Barbadian specimen renders it highly probable that they 

 should be transferred to the upper Cenozoic. 



The paucity of American Pliocene echinoidea is to be regretted, as those of this 

 age in Europe have been in most cases carefully collected and monographed. With 

 the few Pliocene echinoids from America they have nothing in common; but as 

 the writer has pointed out in a recent "Revision of the British fossil Cenozoic 

 echinoidea," those of the English Crag have many affinities with the existing 

 fauna of the West Indies. The Crag echinoids number 22 species, and may be 

 divided into two groups : (1) the common northern European forms, or species 

 closely allied to these ; and (2) a group of genera represented together elsewhere 

 only in the West Indian area. Thus, in the English Crag there are species of 

 Tniiiirchiiiiis, Agassizia, Rhynchopygus, and Echinolampas, of which the nearest 

 allies are Caribbean species. Now, these are all either tropical or littoral forms, 

 and it is of interest to note that they do not occur elsewhere among the European 

 Pliocene deposits. The fauna which agrees besl with that of the English Crag 



