MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 381 



The habits of the hermit crabs, though secondarily acquired iu comparatively recent times, 

 have had no tendency to shorten the larval period. This is also true of the Pinnotheres, Simi- 

 larly the couituensalisin of such forms as Ponton ia domest-iva, which lives iu the mantle cavity of 

 several species of Piuua, has in no way affected its development. 



IV. THE ADULT. 



The Alpheus whose development has just been traced was provisionally named Alpheus prw- 

 cox (1W), in allusion to its greatly accelerated metamorphosis. It has since been found to agree in 

 most particulars with the description and figure of Alphciix mtitlv-yi given by Guerin iu Kaniou de 

 la Sagra's History of Cuba (18). IIP Gueriu's drawings the long spine (squama! spine) of the 

 anteun;e is represented as continuous throughout its length with the scale, and the carpus of the 

 second pair of thoracic legs as divided into three segments. The segmentation of the carpus of this 

 appendage is one of the most constant of specific characters. If these figures are accurately 

 drawn, the two forms iu question are certainly not specifically identical ; but though not at first able 

 to satisfy myself on this point, or to decide from the short aud imperfect description, it seemed 

 best after further study to adopt Gueriu's name. 



The systematic zoology of the genus Alpheus is in a very unsatisfactory state, and in the 

 absence of adequate and well executed drawings, aud too often with only vague or general descrip- 

 tions, the attempt to identify the less kuovvu species is apt to be attended with most doubtful 

 success. 



It is now necessary to complete the account of the metamorphosis of this Alpheus by giving 

 a description of the adult form. The Alpheus saulcyi resident in certain green sponges found on 

 the Bahama reefs is regarded as the typical form of this species. 



DIAGNOSIS. 



Carapace ends anteriorly in three spines. The median spine or rostrum inclined, especially in the 

 female; arises from the edges of the carapace, like the lateral or orbital spines; barely surpasses the latter 

 in length ; without keel. Body and appendages generally smooth ; large chela slightly twisted, smooth, no 

 transverse constrictions ; small chela subcylindrical, short ; dactyle nearly straight, slender, one-half as long 

 as propodus ; carpus of this appendage short. Aural spine of inner antenna variable iu length ; rarely sur- 

 passes the middle of the second segment. Basal segment of outer antenna is produced into an outer, inferior 

 spine, and an upper rudimentary spur ; articulated with it is a squamal spine, on which is developed a con- 

 spicuous scale. Carpus of second pair of thoracic legs superficially segmented into five parts. 



SPECIAL DESCRIPTION. 



Length : Smallest found in green sponges, 9.5 mm , S ; largest, 42"" 11 , 9 ; average length, 25 to 

 30 mm . Females exceed the males a little in length, and greatly surpass the latter iu size when 

 swollen with their eggs. 



Color: The color of this form is shown iu PI. iv. Large claw vermilliou above, fading out 

 towards proximal half, aud nearly colorless below. On upper face of claw, a transverse colorless 

 band is often seen. Small chela often tinged with red, also the terminal segment of the third pair 

 of maxillipeds. Uody, pale, translucent, with scattered cells of reddish or yellow pigment, subject 

 to quantitative variation, and visible to the naked eye on close inspection or by aid of a lens. 



A young male which was kept for several days iu an aquarium molted and lost completely the 

 bright color of its claws. Sexes are colored alike, excepting the eggs and ovaries of the female, 

 which are bright green. 



In one or two instances a pair of these Crustacea were found which exhibited a variation from 

 these tints. In these cases the male aud female were of light-reddish orange and the claws deep 

 orange red, darkest on the " fingers" ; eggs aud ovaries of female golden yellow. Length of 5 , 33 IUU1 . 

 Number of eggs attached to abdomen, 347. The male in this case also, after a moult, was apparently 

 colorless, contrary to the rule that upon molting the colors are enhanced. . 



The carapace, is smooth, translucent, and, like the abdomen, takes on more or less the hue of 

 the yellow or green ovaries. It ends anteriorly iu a trident, formed by the median rostrum and 



