78 THE NAUTILUS. 



I can find no reliable feature by winch to separate the American 

 4> monodactyl " species (the posterior lobe, which is derived from the 

 shoulder-angle and is not homologous with the digitation of the 

 Oriental tonus, being incipient in gigas itself), and I have detected 

 the peculiar periostracum in all hut gallus. Moreover in the char- 

 acters <>t' spire and body gallus agrees with gig as, bitnberculatus with 

 costaius (and has a variety corresponding with inermis), and peruvi- 

 anas with galeatus, and this accords witli their geographical range. 



Si ib -(/roup 02. 



Canai short, straight ; lip scarcely expanded, with margin faintly 

 incurled, deeply receding at the suture, and not surmounting the 

 shoulder of the penultimate whorl ; body nearly smooth ; periostracum 

 finely, densely, vertically lamellose; inner lip spreading. 



S. pugilis, gracilior. 



Antillean and West Mexican. 



The last clause of the definition is needed to distinguish this small 

 American group from Gonomurex luhuanus, which it strangely par- 

 allels. Only a conservative spirit and the occasional presence of 

 wave-^triolations on the periostracum induce me to give this group 

 secondary rank under group C. 



Group D (Evprotomus). 



Canal very short, with the dorsal margin produced beyond the short 

 tip of the straightened columella; lip with the antesinual lobe broad, 

 rolled upward and inward, the outer margin broadly and abruptly 

 inflected ; body with a large node ; spire high, wdiorls nodulous. 



S. laciniatus, latissimus, ponderosus, taurus. 



Distr. ; Japan to Fiji Is. 



S. tricornis. Red Sea. 



The last species is aberrant in its single posterior lobe and obso- 

 lescent inflection of the lip margin, but the resemblance to peruvianas 

 is evidently deceptive. S. taurus strikingly emphasizes the close al- 

 liance of this group to 



Group E {Pterocera). 



This group need not be redefined. It has the peculiar form of 

 antesinual lobe of the preceding group, and differs mainly in the 

 elongated canals and numerous lip-claws. 



{To be continued.) 



