492 Prof. Wyville Thomson on the Echinidea of the [June 20, 



due to our wider knowledge of the fauna of the shallower water ; from 

 300 to 800 fathoms along the coast of Britain many species of all the 

 orders are enormously abundant, so much so as to give a very marked 

 character to the fauna of that special zone. Several of these species, 

 such as Cidaris papillata, Leske, Toxopneustes drobachiensis, Midler, 

 Echinus norvegicus, D. & K., Astropecten tenuispinus, D. &K., Archaster 

 Parellii, D. &K., A. Andromeda, M. & T., and Euryale Linkii, M. & T., 

 have been long known to inhabit the deep water of the British area, and 

 form part of a fauna which will be probably found to have a very wide lateral 

 extension at temperatures whose minimum ranges from 0° C. to + 2° C, a 

 fauna which crops up, as it were, within the ordinary limits of observation in 

 the seas of Scandinavia, and which has consequently been carefully studied 

 by the Scandinavian naturalists. 



Another group of species, including Tripylus fragilis, D. & K., Cteno- 

 discus crispatus, Retzius, Pteraster militaris, M. & T., Amphiura abyssi- 

 cola, Sars, Antedon Eschrichtii, O. F. Midler, and several others, are members 

 of the same fauna described from localities in the seas of Scandinavia and 

 Greenland, but not hitherto known as British. A third section, consisting 

 of a number of undescribed Echinideans, Asterideans, and Ophiurideans, 

 may probably also belong to this fauna ; while a fourth group, likewise 

 undescribed, and including such forms as Porocidaris, Phormosoma, Cal- 

 veria, Pourtalesia, Neolampas, Zoroaster, Ophiomusium, Pentacrimis, 

 Mhizocrinus, and Bathycrinus, would rather appear to be referable to a 

 special deep-sea fauna of which we as yet know only a few examples, and 

 with whose conditions and extension we are unacquainted. This abyssal 

 fauna is of great interest, inasmuch as nearly all the hitherto discovered 

 forms referred to it show close relations to family types of Cretaceous or 

 early Tertiary age, and hitherto supposed to be extinct. 



Twenty-seven species of Echinidea were procured during the cruises of 

 1868, 1869, and 1870, off the coasts of Britain and Portugal, at depths 

 varying from 100 to 2435 fathoms. 



ClDARID^E. 



Cidaris, Lamarck. 



1. C. papillata, Leske. 



Occurs in enormous numbers on gravel at depths from 100 to 400 

 fathoms, from Fseroe to Gibraltar, and small-sized examples are frequent 

 down to 1000 fathoms. This is a variable species, and every possible 

 link may be shown between the typical C. papillata, Leske, and C. hystrix, 

 Lam. I have no hesitation, after examining many hundreds of specimens, 

 in fusing the two forms into one species. 



2. C. affinis, Stokes. 



This is a pretty little species, and apparently distinct, although it is some- 

 times not easy to draw the line between it and small forms of C. papillata. 



