438 ME. J. E. HENDEESON— A CONTEIBUTIOJST 



the east coast of the United States. The Tozeuma serratum of A. Milne-Edwards, from 

 the West Indies, is probably, as Bate has remarked, referable to some other genus, for 

 in it the carpus of the second legs is multiarticulate. 



Genus Rhynchocinetes, Milne-Edwards. 



257. Rhtnchocinetes rugulosus, Stimpson. 



R. ru(juhsus, Stimpson, Proc. Acad. Nat. Sci. Philad. Jan. 1860, p. 36. 



Tuticorin, four specimens {Thurston). 



The body is marked dorsally by fine transvei'se or somewhat concentric impressed 



striae. The rostral formula in three specimens is — ^ — ^, and in the fourth — ^ — -, the 



first three upper teeth being situated on the carapace ; whereas according to Stimpson 

 the rostrum is tridentate above near the apex, and has twelve teeth below. These 

 differences may be due to local variation, or possibly tlie Tuticorin examples are refer- 

 able to a distinct and new species, but I do not venture to separate them. A few 

 spinules are present on the meral joints of the last three pairs of legs, and the first pair 

 have a spine at the ujoper distal end of both the merus and the carpus, while the latter 

 joint is carinated superiorly along its entire length. The ajDex of the telson is acuminate, 

 and carries two pairs of subterminal spinules, of which the inner pair exceed the terminal 

 portion of tlie telson, and are about three times the length of the outer pair. 

 Distribution. Port Jackson (Stimpson). 



Genus Pontonia, LatreiUe. 



258. Pontonia tuidacnae, Dana. 



P. tridacnae, Daua, Crust. U.S. Explor. Exped. pt. i. p. 571, pi. xxxvii. fig. 1 (1852). 



( = Conchodytes tridacnae, Peters) . 



Tuticorin ( Thurston) ; Rameswaram, in the mantle-chamber of a large Pinna 

 [J. R. H.). 



Distribution. Ptcd Sea {Hilgendorf) ; E. Africa {Peters, Ililgendorf) ; N. and N.E. 

 Australia {Iliers); Samoa (Dana, Ortinann) ; Eijis (Miers). 



Genus Leander, Desmarest. 



This genus was founded by E. Desmarest in 1849 (Ann. Soc. Ent. de France, ser. 2 

 t. vii. p. 91), but poorly characterized, most stress being laid on the gibbosity of the 

 abdomen; indeed, the characters furnished by this writer might apply to either the fresh- 

 water or the marine forms. He, however, figures as the type an undoubted marine form, 

 L. erraticAis, Dcsm. {=L. natator, Milne-Edw. fide Spence Bate). Stimpson, iu 1800, 

 was the first to separate Leander and Palcemon, and to j^roperly characterize them, 

 placing the marine species in Leander and tlie fluviatile species in Palcemon, an 

 arrangement which has been followed by most subsequent writers. Spence Bate, in 

 his Report on the ' Challenger ' Macrura, partially reverses this arrangement and refers 

 the marine species to Palcemon, partly because he regarded Dcsmarest's diagnosis as 

 valueless, and because Leach, Milne-Edwards, Bell, and others had termed the common 



