OPHIURANS OF UNITED STATES NATIONAL MUSEUM. 139 



this specimen here and reproduce (pi. 18, fig. 8) an arm piece, because it shows a 

 pecuharity which I did not observe in the specimens wliich I used as types. In 

 fact, at the level of each brachial article, one of the granules of the upper face is 

 seen to take on a great development and to swell into a large conical nipjde with 

 rounded end, which is verj' conspicuous and very mucli protruding above the level 

 of the next granules. This peculiarity is observed chiefly at the beginning of the 

 arms. I can but mention this special arrangement, whicli might perhaps justify 

 the introduction of a distinct variety, if it were found again on other samples. 

 By all its other characters, this individual may be referred to A. elongatum. 



Connections and dijf'trences. — Among the Astrochema for which A. elongatum 

 might be mistaken, I shall cite chiefly A. clavigerum Yerriil, inomatum Koehler, 

 intedum Lyman, and nuttingii Verrill. The distinction between them will be found 

 in the following characters. 



A. clavigerum has protrading radial ribs, which, however, are widened; the 

 upper face of the disk and arms is covered with small, smooth granules which 

 become only a little stronger on the radial ribs without ofi'ering those inequahties 

 which I notice in the new species. The internal tentacular scale takes on a remark- 

 able development, and it is, besides, swollen at its end in the shape of a club. A. 

 inornaium has wide and Uttle protruding radial ribs, which are uniformly covered 

 with small granules similar to those on the rest of the upper face of the disk; the 

 upper face of the aiTus also is unifonnly granulous and the granules are always less 

 coai-se than in A. elongatum. The arms are shorter and the internal brachial spine 

 is more club-hke toward the end; the second spine always appeai-s a httle farther 

 away than in -4. elongatum, and, as a rule, near the seventh pair of pores. In .4. 

 intectum from Havana, the under face of the arms is altogether bare and as to the 

 tentacular scales there are already two appearing on the pores of the second pair. 

 In A. nuttingii, the pores even of the fii-st pair each carry a tentacular scale, and the 

 second scale appears either on the pores of the second or on those of the tliird pair. 

 The upper face of the aims offers but a bare tegmnent with a few very much reduced 

 granules, which, however, become more distinct at a certain distance from the disk; 

 the under face of the chsk and of the arms is almost bare. The tentacular mouth 

 poi'es each bear a httle distal scale ; the row of oral papillse is more regular and the 

 tentacular scales are longer and narrower. Lastly, the radial ribs seem to be wider 

 and less protruding than in A. elongatum. 



The other species from the West Indies are easily distinguished from A. 

 elongatum. 



