MUSEUM OF COMPAKATIVE ZOOLOGY. 159 



color to a light yellowish brown. The diameter of the disk is 6 or 7 milli- 

 meters, and the spread of the arms about 20 centimeters. 



The common Actinometra of the Caribbean Sea is a singularly protean 

 species, which was obtained at twenty-nine stations during the " Blake " 

 Expedition of 1878-79, and once in the previous season. The " Hassler " 

 dredged it off Barbados ; and it was found by the " Investigator " at the 

 station already mentioned off St. Lucia, and also on the Martinique and 

 Dominica cable. It ranges from 73 to 278, and possibly to 380 fathoms. 

 Not only is it everywhere very abundant, but it presents a most remark- 

 able series of minor variations on one fairly distinct type, to which I 

 must refer the two forms named Antedon alata and Ant. pulchella re- 

 spectively by the late Mr. Pourtales.* These two forms seemed to me 

 at first sight to represent entirely distinct species ; but I have felt 

 obliged to unite them both with one another, and with four others also 

 apparently distinct at first sight. In naming this type I prefer to use 

 the second of the two specific designations employed by Mr. Pourtales, 

 viz. pulchella ; for the other, alata, refers to a character which, though 

 very marked in some individuals, is barely traceable in others. Gener- 

 ally, the type is a true Actinometra, with eccentric mouth and combed 

 oral pinnules ; though Mr. Pourtales gave the name Antedon to both his 

 species, the two genera not being so distinctly differentiated at the 

 time he wrote as they are now. Most of the specimens have 20 arms, 

 or perhaps one or two less; some, however, have as few as 12-15, 

 and there is so little difference between them and a few ten-armed in- 

 dividuals occurring at the same localities that I do not think the latter 

 can be regarded as a separate species. A small Antedon which is toler- 

 ably abundant at five stations exhibits the same variability, and I have 

 met with a few similar cases in the " Challenger " collection. As a rule, 

 however, ten-armed Comatulce are sharply distinguished from those in 

 which the rays divide more than once. Act. pulchella is also interesting 

 as furnishing the third instance which I have met with of a variation 

 from the ordinary type of five rays.f One specimen, like one dredged 

 by the "Challenger," has six rays; while another "Challenger'' speci- 

 men has but four, though in other individuals of each species there is 

 the usual number of five rays. It is curious that this variation, which 

 is common in Rhizocrinus, should be so rare among the Comatuhv. 

 The special characters of this species are as follows : — 



* Bull. Mus. Comp. Zool., Vol. V. No. 9, pp. 215, 218. 

 t Proa R. S., 1879, p. 88S. 



