78 THE NAUTILUS. 



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

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

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

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

 the peculiar periostracum in all but yalhts. Moreover in the char- 

 acters of spire and body gallus agrees with gigas, bitnberculatus with 

 coslalus (and has a variety corresponding with inermis), and pemri- 

 aims with galeatus, and this accords with their geographical range. 



Sub-group C J. 



Canal 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 lamelluse; inner lip spreading. 



S. pu (/His, 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. 



GHOUP 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, whorls nodulous. 



S. laciniatu-s, 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 perun'anus 

 is evidently deceptive. $. 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.) 



