22 BULLETIN 74, UNITED STATES NATIONAL MUSEUM. 



synonyms all the other si)ecies which luul been established, partly by Mr. Agassiz 

 liimseif. In my Siam Echinoidea I undertook a revision of the o;eniis and came 

 to the conclusion that several species oufrht to be tlistin<:uished, which had hitherto 

 been wron<;ly made synonyms of D. setosum, and in their recently published great 

 work Hawaiian and other Pacific Echini; the Salenid^ * * * and Diade- 

 matidse, Agassiz and Clark fully agree with me in regard to both the West Indian 

 form, D. antilUirurn, and the other species. 



In the work mentioned" I made the suggestion that it may perhaps be pos- 

 sible to distinguish the species of Diadema also wiien alive by their coloration, 

 without taking the minor difi'erences in the pedicellarise, etc., into consid- 

 eration. Accordingly I took occasion during a stay in the West Indies in the 

 winter of 1905-6 to examine the living Diadema antillarum. I may then here give 

 a <lescription of its coloration in life. 



From the well-known white spot in the middle line of the interambulacra, in 

 the naked abactinal part of the area, a continuous thin blue line runs down toward 

 the ambitus along either side of the interambulacrum; both lines also continue 

 parallel upward to the anal area, without forming a ring on the apical system. 

 Round the base of all the larger spines there is a fine blue ring: a few small blue 

 spots may occur irregularly on the skin of the test, on the abactinal side, which 

 is otherwise quite black; the blue lines may be very slightly developed; also the 

 white interambulacral spot may be very small. Some specimens may be almost 

 black. The anal tube is black, not reddish toward the end (as is the case in 

 D. saxatile). The actinal side and the peristome are purple. 



Unfortunately the blue color is not kept in the preserved specimens, either in 

 alcohol or formalin, so the coloration cannot be of use for distinguishing the species 

 in a preserved state. Whether all the different species have their own peculiar 

 coloration, can, of course, only be affirmed after observations on the living indi- 

 viduals. In an}^ case, D. antiUarum difTers consi(leral)ly in coloration from D. 

 saxatile, in which there is no continuous blue line along the primary series of inter- 

 ambulacral sjiines, but a series of blue spots, as is shown by the vSarasins in their 

 magnificent i)aper Die Augen und das Integument der Diadematiden,'' and as I 

 have myself had occasion to observe during my stay in Siam. 



This point seems to be well worthy of more detailed investigation, so I have 

 thought it not inappropriate to call the attention of those who are fortunate enough 

 to have easy access to the living animals to the matter. It is quite probable that 

 Wfc may here find valuable facts for the determination of the interrelations of the 

 different species of Diadema. 



REVISED LIST OF THE ECHINOIDS KNOWN TO OCCUR IN THE AMERICAN REGION 

 OF THE NORTH ATLANTIC, AND IN THE WEST INDIES. 



It may prove useful to give here a list of the Echinoids occurring on the 

 American side of the North Atlantic and in the West Indian seas. Though there 

 has been very little new material collected since the Blake and the Albatross 

 expeditions, this list differs veiy considerably from that given by Mr. Agassiz 

 in the report on the Blake Ecliini, the recent researches (by A. Agassiz, 



« Siam Echinoidea, p. 17. 



6 Ergebnisse naturw. Forsrhungon auf Ceylon, vol. 1, 1887, pi. 3, fig.e. 14-1.5. 



