SHALLOW-WATER STARFISHES 43 



ossicles, both on the sides and dorsal surface of the rays, the 

 ossicles themselves being larger, broader, and more rhombic, and 

 usually united in more definite, longitudinal rows, with smaller and 

 more regular intervening papular areas. In either group, as at 

 present understood, the interactinal or ventral plates may have the 

 regular serial and subtesselated arrangement. 



A. GENERIC SUBDIVISIONS OF ASTERIIN^. 



The genus Asterias, in the wider sense, as still used by many 

 writers, includes a very large number and a great variety of species, 

 found in all seas. Various attempts have been made to divide the 

 genus into a number of genera or subgenera on structural char- 

 acters, but hitherto there has been no general agreement among 

 writers, as to the number or limits of most of the subdivisions. Nor 

 do I flatter myself that my own views will be altogether acceptable. 



One of the best known classifications hitherto proposed is that of 

 Sladen.^ 



He admitted, in the restricted family Asteriidse (our Asteriinae), 

 five distinct genera, including Pycnopodia. Under Asterias he had 

 six subgenera. Most of these are undoubtedly worthy of generic 

 rank. One of them (Leptasterias) had been proposed as a genus by 

 the present writer, many years earlier, and another (Stolasterias) is 

 essentially identical with our Coscinasterias, 1867. His subgenus 

 Hydrasterias is evidently a distinct genus, peculiar to the deep seas, 

 and has already been so recognized by Perrier and myself. Perrier, 

 in a later work,'' recognized all of Sladen's divisions as genera, but 

 with the limits modified in some cases, and proposed four more 

 generic subdivisions, some of which seem to have no great syste- 

 matic value. This is particularly true of Diplasterias, separated 

 from Asterias mainly on account of the two regular rows of adambu- 

 lacral spines, — a character that is variable in this group and often of 

 no more than specific importance, taken alone. Many species of 

 Asterias have alternately one or two adambulacral spines, and others 

 have irregularly one and two to a plate. C. tenuispina is generally 

 strictly monacanthid, but unusually large specimens usually bear two 

 spines on a few of the plates proximally. 



Perrier, in the article referred to, recognized fifteen genera in the 

 family. 



^Voyage Challenger, Z06I., xxx, pp. 560-564, 1889. 



'Exped. Scientif. du Travailleur et du Talisman, Echinodermes, pp. 108, 

 109, 1894. 



