76 



Papers from the Department of Marine Biology. 



Coutiere goes on to remark that his group is 



"differentiated from the other groups by some marked characters, which are 

 almost all characters found in the Hippolytidse and therefore suggest a less 

 strong resemblance to the Reptantia; as frequently happens, there are added 

 to these primitive characters (others) which show on the contrary, an adapta- 

 tion carried very far; for instance, the strongly curved hooks and the movable 

 finger of the small chela surpassing the fixed finger; these characters are espe- 

 cially marked in S. comatularum and are explained by its commensalism with 

 the comatulid, being implements of attachment for the Synalpheus." 



Both the species which I have collected belong to this group. More- 

 over, two other forms which are included by Coutiere are distinctly 

 stated in the original descriptions as occurring on crinoids. These are: 

 Synalpheus slimpsonii var. maldivensis, and Synalpheus carinatus var. 

 binongeensis (from Comatula). 



Thus, 4 out of the 12 species and subspecies in the group possess this 

 habit. As, for the most part, the different forms are only known from 

 very few specimens, and notes on the habits or even colouration of the 

 living animal are hardly ever given, I think it highly likely that exten- 

 sion of our knowledge will show that the whole group is characterized 

 by commensalism with crinoids and possibly also by the striking 

 colouration, so different from that of other alpheids, which are found in 

 S. brucei and S. comatularum. 



Synalpheus brucei sp. n. (Plate 1, Fig. 2.) 



A Synalpheus of medium size, commensal on crinoids. Body rather slender, 

 colouration variable, with longitudinal bands of red or purple pigment. Ros- 

 trum very long, about one-third the length of carapace, reaching to the end 

 of second antennular article, 

 slender and acute, continued 

 backwards for a short dis- 

 tance beyond the level of the 

 eyes as a low carina. Sup- 

 raorbital spines acute, about 

 one-third the length of the 

 rostrum. Antennae (2) very 

 long and slender; the basal 

 joint hardly so long as the 

 spine of the scaphocerite. 

 Antennae (1) very much 

 shorter than antennae; stylo- 

 cerite only reaches to end of proximal article ; proximal article much longer 

 than other two; spines of basicerite almost equal, external does not extend 

 further forward than supraorbital spine. Incisor process of mandible tends 

 to end broadly, with several teeth. Large chela with rather inflated propo- 

 dite, carpopodite with prominent spine on outer border. Meropodite with 

 two smaller spines. Small chela with dactylopodite not stretching beyond 

 end of thumb, meropodite with prominent spine on outer border. First seg- 

 ment of carpus of second pair of feet much longer than the four succeeding 

 segments together. Third and fourth feet armed with sharp spine on inferior 



FIG. 1. Chelse of Synalpheus. 



8. brucei: A, large chela, X 4; B, small chela, X 8. 

 S. comatularum: C, small chela, X 8. 



