■^^ PROOEEDTNOf^ OF TTIE NATIONAL MUSEUM. vol. xxxvi. 



To return to the groups of species of the genus Synalpheiis, the one 

 which I designate by the name of the Paulsoni group, presents a 

 most remarkable geogi'aphical distribution. S. jmidsoni Nobili (per- 

 haps identical with S. tricuspidatus (Heller)) is a species with short 

 carpocerite from the Red Sea and the Persian Gulf, the affinities of 

 which are to my mind very clearly indicated; it is separated, first 

 from the forms with carpocerite equally short, but distinguished by 

 the spinous palm of the large chela, or by the basicerite almost un- 

 armed above, and again from the forms with carpocerite more elon- 

 gate; variation in this last direction leads to some forms with the 

 carpocerite elongate and slender {S. hitlulensis Coutiere, S. tumido- 

 mmius Paulson, the latter very distinct on account of its large eggs, 

 producing mysis, and the spinous angles of the telson). In another 

 direction there are found some forms in which the carpocerite is 

 elongate as in those preceding, but, in addition, is swollen, and of an 

 ovoid form {jS. acanthitelsonis Coutiere, S. hastilicrassus Coutiere). 

 In a third direction, finally, there are found some species differing 

 from S. pauJtioni by the more massive aspect of the appendages; 

 though indicated by a form kurracheensis, this evolutional tendency 

 is more accentuated in the species /S. Idtmtei from Australia, which 

 occurs without change in Chile, and which is also represented in 

 Brazil by the form tenuispina. In Australia again, the species S. 

 m,aecidlochi Coutiere differs most markedly from S. paulsoni kur- 

 racheensis by the presence of large eggs producing mysis. 



There are found forms derived from S. paulsoni at the Mascarene 

 Islands and on the west coast of Africa, of which I have been able to 

 study very unusual specimens from Cape Lopez and from Cape 

 Verde ; these are not strictly typical specimens, but can be separated 

 only by careful study, and it is ini})ossibl(B for me to make them dis- 

 tinct species, in spite of the great actual geographical isolation, which 

 'can probably be considered as absolute. 



On the American coasts are found exactly the same evolutional 

 tendencies in this group ; jS. paulsoni and the other Indo-Pacific forms 

 are not represented there by identical forms, but the differences are 

 at times so slight that, without indication of locality, the identifica- 

 tion would be very difficult. S. lockingtoni differs from S. j)aidsoni 

 almost solely by the spine of the scaphocerite being longer in the 

 latter and surpassing the carpocerite ; with the exception of the ]ilace 

 of origin, the second species would correspond to the " oxyceros " form 

 so often met with that it appears to be almost a constant variation 

 among the subspecies of a given species." 



" It is more convenient and expressive to designate by the name " oxyceros " 

 every subspecies showing tliis variation, but in deference to the accepted rule 

 of nomenclature which forbids duplication of names within a single genus, I 

 have in this paper used different names having a similar meaning, as longi- 

 cornis, elongatus, productus, prolatus, extentus. 



