REPORT ON THE CRUSTACEA MACRURA. 



541 



Observations. — The genus may be divided into three divisions — 



A. Those without rostrum or supraorbital teeth. 



B. Those with rostrum but without supraorbital teeth. 



C. Those with rostrum and with supraorbital teeth. 



This arrangement, however, can only be considered as convenient for purposes of 

 classification, since the above characters are found to exist in various degrees, and 

 Mr. J. S. Kingsley, 1 in regard to Alpheus minus, Say, says : — " In some specimens the 

 ocular spines are present, while the rostrum is wanting ; in others the front is truncate, 

 no spines being present. The proportions of the joints of the carpos of the second pair 

 of pereiopoda also vary," and he continues " the relative lengths of rostrum and ocular 

 spines can be of no great importance when they vary as I have shown." 



If these observations of Mr. Kingsley be justified by further experience of this 

 intricate genus, then many of the recorded species must be merely varieties. For 

 instance, Dana" considers his species of Alpheus leviuscidus, of which I have figured 

 (PL XCVIII. fig. 1) a variety, to be itself only a variety of Alpheus edwardsii, and says 

 further that it is near to Alpheus bi-spinosus of de Haan, which de Haan considers a 

 variety of Alpheus avarus of Fabricius, but which Stimpson affirms to be distinct. 



Alpheus avarus, Fabricus, appears to be not very distinct from Alpheus edwardsii 

 of Audouin. Yet the figure given in this Report of Alpheus leviusculus bears but little 

 resemblance to Audouin's figure of A Ipheus edwardsii. 



Again, some of the species correspond in almost every point except in the presence 



1 Bull. U.S. Geol. Survey, vol. iv., No. 1, p. 191, 1878. 



2 U.S. Explor. Expetl., Crust, p. 543, pi. xxxi. fig. 3. 



