448 EEV. E. BOOG WATSON ON THE 



46. Plettbotoma (Thesbia) dyscbita, n. sp. (SvcncpiTos, of 

 difficult determination.) 



St. 23. March 15, 1873. Lat. 18° 24' K, long. 63° 28' W. 

 Sombrero Island, St. Thomas, Dan. W. Indies. 450 fms. Globi- 

 gerina-ooze. 



Shell. — Thin, white, narrowly oblong or fusiform, with alongish, 

 scarcely" tumid body-whorl, a shortish, conical, convexly whorled, 

 small-pointed, shallow-sutured, conical spire, and a long conical 

 base. Sculpture. Longitudinals — there are delicate thread-like 

 curved lines of growth, which are strongest near the top of the 

 whorls. Spirals — the whole surface is equably covered with fine, 

 faintly raised, rounded threads ; they are slightly fretted by the 

 longitudinals ; between them are little rounded furrows of about 

 twice their breadth. Colour : the spiral threads are porcellaneous, 

 the furrows translucent white, and the surface is a little glossy. 

 Spire rather short, conical, but slightly concave, with hardly any 

 interruption in its profile-lines by the very slightly impressed 

 suture and convexity of the whorls. Apex consists of 2| rounded 

 subcylindrical whorls rising to a small rounded point, where the 

 extreme tip hardly projects and is bent down on one side; it is 

 smooth and glossy, but retains traces of a ruddy epidermis with 

 minute spiral threads. Whorls 6 in all, of regular but rapid 

 increase, rather high and broad, convex, but sloping, and not 

 tumid ; the last is very long and full, though not tumid ; and 

 there is little contraction on the long conical base. Suture slightly 

 impressed, rather oblique. Mouth large, open, and oblong, pointed 

 above, scarcely contracted below, but truncated at the end of the 

 broad open canal. Outer lip : very equably curved in both its 

 planes ; it has a somewmat high and prominent shoulder above, 

 between which and the body -whorl lies the rather deep, wide, 

 rounded sinus. Inner lip : a thin glaze on the body and out on 

 the long pillar, which is cut off in front with a long, thin, twisted, 

 oblique edge. H. - 35. B. 016. Penultimate whorl, height 

 0-8. Mouth, height 022, breadth 0-08 (?). 



This beautiful little shell, though enclosed in a small glass 

 tube, was found sadly broken, so that the measurement of the 

 breadth of the mouth is slightly doubtful. It is very like P. fra- 

 gilis, Reeve ; but in that species the spirals are stronger and more 

 remote, and the longitudinals much sharper. Defrancia Magella- 

 nica, Phil., is even liker, but is a much stronger shell, has a shorter 

 mouth, below the suture the upper whorls there are contracted 



