20 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



of the specimens of S. hempMlli longicorriis bears ca movable spine 

 on one of the meropodites of the third pair; it is the reappearance, 

 very interesting*, of a character present in many of the Neomeris 

 species (Indo-Pacific), which seems to have disappeared in the 

 American species, even those most like the preceding. It is not a 

 " mutation " permitting one to understand the process by which 

 a new form is originated ; third, a specimen of S. minus possesses on 

 the anterior border of the palm of the small chela a spinous tubercle 

 as on the opposing chela ; this is a " mutation " which is not absolutely 

 rare in the Alpheidfe, and which I have seen even carried so far as 

 to result in the complete symmetry of the two claws of the first pair 

 in a very curious specimen of AlpheiiH dentipes Guerin. But the 

 Alpheidffi have originated from forms with symmetrical claws ; there, 

 again, it is the question of the recurrence of a remote character, and 

 not the indication of a new evolutional line; fourth, some specimens 

 of very small size of S. lonr/icarpus, and of S. hrooksi also, have only 

 four seg-ments in the carpus of the second pair; this detail character- 

 izes the species S. rathhuna^, which is far from being the nearest to 

 S. hrooksi, but it characterizes also the genus Ai^ete, the relations of 

 which with the genus Syaalpheus are truly very remote. 



Concurrent with these facts, obvious, but without importance, may 

 be cited other facts of greater w^eight but without proofs. The char- 

 acters of the subspecies S. hrooksi strepsiceros, S. herricki dimidiates, 

 S. herricki cmgustipes, and of S. tanneri, occurring either among a 

 series of typical specimens or in some localities where the typical 

 specimens also occur, make one think of some " mutations ; " it is, in 

 fact, as I have said before, the case in the entire L.t^vimanus group; 

 close relationship, a general resemblance of the forms which make 

 part of it, but a great variety of combinations of a small number of 

 characters, of which one at least is absolutely constant, certain combi- 

 nations rarely realized, while others are frequent— even taking into 

 account certain errors in the appreciation of the scarcity or the fre- 

 quency of the type — a distinct aspect and clear-cut, though slight, 

 differences. These are mere impressions without proofs, but which, 

 I believe, would occur to every naturalist who has been able to study 

 in its entirety so homogeneous a group; and it would certainly be 

 interesting to attempt for a few of the species of the L.evimanus 

 group some " pure cultures," continued during several generations, 

 supjDosing that one might surmount certain considerable difficulties 

 involved in such an attempt. 



This work, in which the greater part of the forms described are 

 new, necessarily allows of very few bibliographical references; those 

 pertaining to the species of Say, Herrick, and Lockington, the names 

 of which I have been able to retain, are given with the descriptions 



