A NEW COSTA RICAN AMPHIPOD. 



By Thomas R. R. Stebbing, 



Fellow of the Royal Society. 



This new species is interesting- on its own account b}^ reason of the per- 

 fectly chelate second g-nathopods in the male sex, and it makes a further 

 claim to attention )\y apparently throwing light on Fritz Miiller's im- 

 perfectly described Orchestra darwlnii. Since Miiller made no men- 

 tion of the female, it remained doubtful whether his species belonged 

 to OreJiistht or to Talorchextla^ and a comparison of its second gnatho- 

 pods with those of Talorchestia deshayesii{KvidiO\xm)g2iyQ some support 

 to the suspicion that it really belonged to the latter genus. Now, how- 

 ever, its close affinity with the new species from Costa Rica makes its 

 position in Orchcxf/a by far the more probable hypothesis. A compari- 

 son of Midler's figures of two forms of the second gnathopod in the male" 

 with the figures and description of that limb here given, wdiile showing 

 the points of agreement between the two species, will also make clear 

 their very definite distinctness. 



It may be remarked in passing that the separation of TaJorcJie^tla^ 

 Dana, from Nicolet's Orchestoldea^ rests on a rather nai-row founda- 

 tion. In the former genus the first gnathopod of the male must be 

 su])chelate, in the latter it nmst be simple. But there are subtle grada- 

 tions, and in consequence a difl^'erence of opinion sometimes arises as 

 to whether the ditference in nature is present or absent. It is not 

 necessary here to argue the point. 



Family TALITKID.E. 



ORCHESTIA COSTARICANA, new species. 



Plate XI. 



The new (Jcchefitta is of slender structure, strongly compressed, with 

 a shining surface. The second and third side plates have the lower 

 hind angles a little produced l)aclvward. The front lobe of the fifth 

 side plate is as deep as the plate preceding it. The quadrate postero- 



« Facts for Darwin, translated by Dallas, 1869, p. 26. 



Proceedings U. S. National Museum, Vol. XXXI— No. 1490. 



501 



