6 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



with CallistocMton. With such a disposition of the group the inves- 

 tigations which I have thus far made do not lead me to concur, even 

 though I can as yet suggest no better arrangement. It would not 

 be surprising if Lepidozona should later on require elevation to generic 

 rank, but for the present it is perhaps best to leave it where originally 

 placed by Pilsbry. 



ISCHNOCHITON (LEPIDOZONA) AMABILIS, new species. 



Plate 3, figs. 6-7; plate 4, figs. 4-7; plate 5; figs. 1-4. 



Description. — Animal small, elevated, rather elongate; maximum 

 transverse diameter about three-fifths the length, or of shell alone 

 about two-fifths the length. 



Anterior valve rounded, conical; its frontal slope nearly straight, 

 becoming slightly convex on the sides. Interior smooth, marked by 

 about 12 sharp radial lines exactly corresponding to the slits at the 

 margin; teeth slightly roughened at the edge and with rather coarse 

 vertical striations on their outer surfaces (pi. 5, figs. 1-2). 



Median valves elevated, beaked very slightly or even scarcely at 

 all, the slopes distinctly convex. Sutural laminae short and broad, 

 the shallow sinus bridged by a short, delicate, slightly concave plate, 

 barely nicked at the margin to form about 8 very delicate squarish 

 teeth; converging striations or lines corresponding in position to the 

 slits continue back through the substance of the shell, the exact 

 number of both slits and lines being often extremely difficult to 

 determine, though the number appears to become considerably less 

 in the more posterior valves. Eaves spongy and quite short (pi. 5, 

 figs. 1-3). 



Posterior valve with a rather depressed, yet conspicuous, mucro ; 

 posterior region flattened, its slope concave (pi. 5, fig. 4); side 

 slopes convex; sutural plates and intermediate plate similar to those 

 of the middle valves, except that there are only about half as many 

 sHts and lines as in the latter. The lines radiating from the mucro 

 to the posterior slits are practically indistinguishable. The hinder 

 margin is thickened and the central region shows a curious, much 

 branched, triangular callus (pi. 5, fig. 2). 



Anterior valve with 12, intermediate valves with 1-1, posterior 

 valve with 11 slits. 



Entire surface of shell closely and rather heavily granulose. An- 

 terior valve otherwise smooth at the apex, but ornamented below 

 by 33-40 low radial ribs having shallow, not sharply, incised grooves 

 between ; some ribs slightly bifurcating or otherwise rendered indis- 

 tinct, but typically bearing a series of 5 or 6 separate sharply ele- 

 vated pustules; the last series of pustules (4-8) on each side project- 

 ing like teeth from the valve margin. Intermediate valves with 

 lateral areas sculptured like the anterior valve, the 6 or 7 low ribs 

 usually bearing 3-8 pustules each, and the posterior series of 5-6 



