14 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



third, fourth, and fifth feet bearing a third and very obtuse ventral 

 prominence. This prominence, very frequent in the Neomeris group, 

 sometimes becomes a strong triangular hook, but a character still 

 more often met with (with or without the last) is the reduction of 

 the dorsal hook of the dactyl, tlie ventral hook taking the form and 

 thickness of a wooden shoe, as in the curious species S. charonHeWer. 

 The Indo-Pacific region liarbors a large number of species of this 

 group, very easy to distinguish by reason of the characters in the 

 striking form of the dactyls; among them those are especially curious 

 in which exist — or reappear — the rows of spines of the meropodites, 

 so constant in the primitive Eucyphota, and persisting in the 

 Alpheid* only on the propodite. 



These forms of the Neomeris group with spinous meropodites 

 appear to be totally absent from the American coasts. There also 

 the parallelism with the Indo-Pacific forms is carried very far. Be- 

 tween S. hcmphilli Coutiere of Florida and S. mlmuhnsis Coutiere 

 ■ of the Maldives (both of which show an " oxyceros " form) there 

 is no difference except the presence in the latter, and the absence in 

 the former, of the meral spines; and j^et, oddly enough, one quite 

 full-grown specimen of S. he7nphilli^ from the Bermudas, shows on one 

 side only a single meral spine. It is difficult to record such ob- 

 servations without thinking of a common origin for the two species, 

 so completely separated at the present time, and yet so strictly 

 parallel. 



Another species, S. fritzmuUcr'i Coutiere of Florida and the West 

 Indies, exists also in Venezuela and Brazil, where it is represented 

 by the '"'' oxyceros'''' form; it is found again in California with the 

 meropodites more slender. In Ecuador S. nohilu Coutiere, a form 

 in Avhich the meropodites are, on the other hand, shorter and more 

 swollen, replaces S. fritzmulleri. In the Indo-Pacific region, S. hakeri 

 Coutiere, in which the supernumerary ventral prominence is very 

 feeble, is the species most closely allied to the preceding ones. 



Another very striking instance of parallelism is the existence in 

 Lower California and in the Red Sea of the species aS. sanlucas'i 

 Coutiere and S. heroni Coutiere respectively, both characterized 

 by the very massive form of all the appendages. The modes of 

 differentiation of the species are again repeated. A form being 

 found, for example, with a short carpocerite, one may expect to meet 

 those with a long carpocerite, then those with more slender members, 

 with more massive members, with basicerite spinous above, or not, 

 with large chela unarmed or spinous on the palmar border, those in 

 which the angles of the telson are prolonged in a spine or not, etc. 

 One can not avoid drawing the conclusion that such a constancy in 

 the modes of variation strongly resembles an hereditary tendency, 

 due to the small number of species from which the genus Synalpheiis 

 must have sprung. 



