NASSA. 17 



NASSA., I, MIII. 



II. and A. Adams in their kk Genera of Uo"ent Mollusca" have 

 enumerated 210 species of Xassa; Reeve's Monograph in the 

 "Conchologia Iconica" conttiins 182 accepted species and 13 

 synonyms, = 195 names in all. The present monograph includes 

 ;")!).") specific names, of which 131 only are accepted as i>oo<l 

 species, :>(J4 are relegated to the synonymy of these, and 100 arc 

 undetermined for want of illustrations or specimens. The dis- 

 tribution of the genus is world-wide, except that no specimens 

 exist in the icy seas near the poles where they appear to be 

 replaced by the Bnccinnms. They occur principally in the waters 

 of tropical and subtropical latitudes. 



The fossil species are few in number, commencing with the 

 Eocene formation. For some of the American fossils Mr. T. A. 

 Conrad has proposed distinct generic names, but their separation 

 from Xassa is scarcely advisable. 



The animal of Xassa has a broad head, and a foot qnadrately 

 expanded in front, with the corners often pointed, whilst behind 

 it bifurcates and is prolonged frequently into two subulate tails. 

 The operculum is usually serrate on the margin but is sometimes 

 plain. The Xassre are very active, and not at all shy when kept 

 in confinement. They may be occasionally seen floating with 

 the foot upwards. They are predaceous, feeding on other mol- 

 Insks, the shells of which they bore. I have frequently seen the 

 shells of the American species themselves bored, the hole being 

 of such a size as to suggest cannibalism. Perhaps the avenger 

 of their misdeeds is a beautiful and very active hermit crab 

 which disports itself in the Nassa's shell, immense multitudes 

 being seen at low tide in the water near the shore line. Whether 

 begged, borrowed, stolen, or lawfully captured by the red right 

 claw, it is certain that, at Atlantic Chy, Xew Jersey, the hermit 

 inhabits a vast majority of the specimens of Nassa occurring to 

 the collector. Although roost of the species are littoral, a few 

 have been collected at considerable depths; the undescribed N. 

 brychia, Watson, was dredged at (>20 fathoms by the " Challenger 

 Expedition." Some of them have been observed to spring 

 up and throw themselves over on being suddenly disturbed. 

 Usually they glide along the surface of the mud, leaving a track 

 indicating their line of inarch, at the end of which is a small 

 3 



