202 



ON THE TOPOGRAPHY AND GEOLOGY 



M. a n t i 1 1 a r u m. G al)b, n. s. 



Shell broadly fusiform, whorls eight, rouuded, varices three, small, having small, sharp spines variable in number ; 

 body whorl inflated, rounding in broadly to the suture, without any marked angle above, below tapering convexly 

 to a nearly straight, short canal ; spire elevated, about as long as the mouth, less the canal. Surface ornamented 

 by numerous, more or less alternating, acute, revolving ribs, with concave outer spaces ; crossing these are rather 

 indistinct longitudinal ribs, four or live between each pair of varices. These ribs are better marked where they 

 cross the revolving lines, than in the interspaces. Nuclear whorls polished, rounded and without ornament. 

 Aperture ovate, constricted in advance, canal about equal in length to that of the mouth proper. Inner lip expanded, 

 showing transverse striations ; outer lip more strongly striate internally. Length 1.15 in.; width .75 in. 



A rare shell whose rounded form, thinner structure, more delicate varices and 

 sculptm-e, and smaller size will all serve to distinguish it from the two preceding. 



M. (Chicoreus) megacerus. Sby. Proc. Zool. Soc, 1845. Rve. No. 24. - 



Living on the coast of Santo Domingo. > - . 



M. (Ptcronotus) t e x t i 1 i s. Gabb. n. s. 



Shell compressed triangular ; whorls eight, the first nuclear, the next three cancellate and showing little or no 

 trace of varices, which show themselves on the next (fifth) distinctly for the first time, suture deep, caused by the 

 great -convexity of the whorls. Body whorl broad and flat above, then very convex near the top and tapering very 

 gradually in advance. The three varices are thick at their bases, broad, acute and slightly recurved on the margin. 

 Between each pair of varices there is one large prominent node, placed hjngitudinally, too broad to be called a rib. 

 The entire surface is covered by about a dozen revolving ribs, except on the faces of the varices, where correspond- 

 ing grooves take their places. Crossing these, the lines of growth are developed into minute erect plates, placed at 

 equal distances and arching over all the ribs and intermediate, alternating lines, so as to produce under a lens, the 

 effect of a lace, or loo.sely woven web. Aperture small, ovate ; inner lip acute ; outer lip faintly grooved internally ; 

 canal about twice as long as mouth and nearly, or entirely arched over. Length 1.4 in.; width .8 in. 



M. (Ptcronotus) c o m p a c t u s. Gabb. n. s. 



Shell short, thick, robust ; spire about two-thirds as long as body whorl. Whorls eight ; the first two nuclear, 

 suture impressed. Body whorl broad above, tapering in advance, top sloping, very slightly concave. Varices three, 

 short, robust, fimbriated or toothed on the margins, but bearing no spines or other elongate processes. Between 

 each pair of varices, on the shoulder of the whorl, is a broad, blunt node. Surface ornamented by numerous large 

 revolving ribs, between which are many smaller lines, all crossed by distinct, subsquamose lines of growth. Apei ture 

 small, sub-oval, iinier lip with a faint tooth posteriorly ; outer lip internally striate ; canal short, blunt. Length 

 2.3 in.; width 1.4 in. 



The spire is much highei- in the preceding species, and this is altogether a much 

 heavier and more compact shell. 



TROPHON. Montf. 



T. d o m i n i c e n s i s. Gabb, n. s. 



Shell small, broadly fusifoim, tl^in ; spire three-fifths the length of the mouth, turriculated ; whorls eight, the 

 first three nuclear, round and increasing very little in width, the other five widening more raj)idly and angulated. 

 Body whorl truncated above, with a rounded rib on the angle ; above this the surface sinuous, convex nearest the 

 suture and concave adjoining the angle ; below the angle it is convex in the middle and rounds concavely into a 

 moderate canal. Surface marked by from six to seven blunt varices, each bearing a single spire on the angle of the 

 whorl. Between the varices the surface is shallowly excavated. Crossing both the varices and interspaces, below 

 the angle, there are a few small revolving ribs. Aperture bi-angular posteriorly, narrowed gradually in aiLvance ; 

 canal moderate in length, open ; outer lip denticulated internally. Length .8 inch. 



A very rare shell. But two specimens were found. 



