336 bulletin: museum of comparative zoology. 



several months but at the end of a year have faded very much. 

 Liitken's description and figures fit these Tobagoan specimens admir- 

 ably but Dr. Mortensen has kindly compared one of them with Liit- 

 ken's type and assures me there is no doubt of their identity. 

 The remarkable fragmentation of the upper arm-plates in this species 

 and 0. guttatum should probably be considered a generic character, 

 especially as it is associated with a peculiar type of disk-granulation. 



Ophiocryptus dubius, sp. nov. 

 dubius = doubtful, in reference to the uncertainty of its status. 

 Plate 3, fig. 4, 5. 



HoMype.— M. C. Z. 4,171. British West Indies: Tobago, Buccoo 

 Bay, April, 1916, under a stone in very shallow water. Carnegie 

 Expedition. H. L. Clark coll. 



Disk, 4.5 mm. in diameter; arms, about 12 mm. long. Disk 

 covered by a very close coat of fine granules which not only conceals 

 the radial shields and covers the interbrachial areas below, but extends 

 over all the plates of the arms, clear to the tip, completely concealing 

 them, and over all the plates of the oral frame too, except the center 

 of the madreporite. Genital slits 4 in each interbrachial area, small. 

 Oral papillae about 9 on each side, the two distalmost flattest and 

 largest, the most distal extending inwards above the second. Arm- 

 spines 5 (4 distally), very small, thick, almost conical, pointed, well- 

 spaced, not appressed. Tentacle-scales 2, relatively large, the outer 

 not overlapping the base of the lowest arm-spine. Color, in life, pale 

 grayish above, nearly white beneath; upper surface of arms with 

 faint indications of two or three dusky, transverse bands. 



This specimen raises anew the whole question of the relationship 

 of Ophioncus and Ophiocryptus to Ophioderma. Are they based 

 simply on very young specimens of that genus or are they really valid 

 genera? This problem will be solved only when much more material is 

 available. The type of Ophioncus is unique and each of the species 

 of Ophiocryptus is based on a single specimen. At Tobago, I secured 

 many young Ophioderma appressum, with the disks less than 5 mm. in 

 diameter; there is no doubt as to their generic position. On the 

 other hand, I have had the opportunity, through the kindness of Mr. 

 A. H. Clark and the authorities of the U. S. National Museum, of 

 examining the brittle-star which Koehler, (1914. Bull. 84 U. S. N. M., 



