Verrill, Notes on Radiata. 349 



bean Fauna, by a large number of peculiar American genera, hav- 

 ing allied species in each, and by many analogous species in cosmo- 

 politan genera. This close relation between the two faunse may, 

 also, be well shown by the large number of Indo-Pacific genera that 

 are equally absent from both, although widely diffused through the 

 Pacific and Indian Oceans, of which the following are examples . 

 Ophiopcza, Ophiarachna, Ophiomastix, Ophiarthrum^ Ophioplocus 

 Trichaster, Culcita, Anthetiia, Archaster, Nardoa {Scytaster), Goni- 

 ocidaris, Fhyllacanthus, Echinothrix, Scdmacis, Temnopleurus Ile- 

 liocidaris (restricted), Heterocentrotus, Acrocladia, Ifipponoe, Laga- 

 num^ Mumphia, Lobophora, Echinolampas* Maretia, Desoria. 



The apparent absence of Comatulidm and other Crinoidea is, at 

 present, a remarkable feature of the Panamian Fauna. It is quite 

 probable, however, that species of this group will be discovered 

 hereafter, since they occur in considerable numV)ers, both in the Indo- 

 Pacific and Caribbean Faunte, as well as in the temperate and arctic 

 portions of the Atlantic. 



Future discoveries are likely to modify to some extent the details 

 in the distribution of the genera here given, but it is not probable 

 that the general arrangement of the generic types will be essentially 

 changed, or that the conclusions arrived at can be much modified, 

 for species that may hereafter be discovered are quite as likely to 

 belong to West Indian or cosmopolitan genera, as to those peculiar 

 to the Pacific and Indian Oceans. 



In the above discussion the Holothurians have been omitted be- 

 cause quite a number of the species known to me from each fauna are 

 still undescribed, and because there are good reasons for supposing 

 that there are many Panamian forms that have not yet been collected, 

 such as Synapta, Chirodota, and other species that burrow, or seek 

 hiding places. Nor have the Holothurians of other tropical regions 

 been so thoroughly collected as to make detailed comparisons possible. 



To the geologist one of the most interesting questions connected 

 with the study of the Atlantic and Pacific faunae of tropical America, 

 is the possibility of a direct connection of the two Oceans, across the 

 Isthmus, during late geological periods. Such a connection has been 

 suggested by some Geologists, upon theoretical grounds, to account 

 for the coldness of the climate in North America and Europe, during 

 the glacial period. The only direct, geological evidence of such a 

 connection, that has been adduced, so far as known to me, is the 



* Mr. A. Agassiz has described Echinolampas caratomides dredged by Pourtales off 

 Florida, — Reprint. * 



