ART. 9 MOLLUSKS OF THE GENUS ACAR BARTSCH d 



The umbones are fairly closely approximated and leave only a narrow 

 marginal area between them, which is marked by a few fine lines 

 paralleling the margin of the hinge. The anterior end is strongly 

 rounded and the posterior somewhat produced ventrally. The sur- 

 face of the shell is marked by radiating, closely approximated, 

 slender cords, of which at least 15 are present on the anterior end 

 and 21 on the posterior area, and 48 in the middle part. In addi- 

 tion to these cords the valves are marked by concentric lamina, 

 which render the cords nodulose. The sculpture is best visualized 

 by consulting our figures. Interior of shell white, with a buffy tinge. 

 The anterior, posterior, and ventral margins are rendered dentic- 

 ulated by the external sculpture. The hinge teeth are small in the 

 center and increase in size toward either extremity, becoming some- 

 what irregular toward the extremities. In the main the anterior 

 slope anteriorly and the posterior posteriorly, but the early posterior" 

 teeth have a somewhat triangular shape, while the anterior ones 

 are somewhat irregular. Both of them increase in size from the 

 median portion outward. Fourteen appear to be present both in the 

 anterior and posterior half of the hinge in the specimen figured. The 

 muscle scars are large, smooth, and strongly elevated. 



We have many specimens of this species, which seems to range 

 through the entire Mazatlanic faunal area, and also appears to ex- 

 tend up on the outer coast of Lower California to Point Abreojos. 

 The specimen that I have figured is one of a small series from 

 Mazatlan, the type locality. 



T7/pe.—\J.S.^M. No. 382428. It measures: Length, 23.8 mm.; 

 height, 12.7 mm. ; diameter, 12.6 mm. 



Remarhs. — Sowerby says that " this elaborately ornamented shell 

 looks at first sight like a piece of Chinese carving. From Mazatlan." 



This species resembles most nearly the Panama forms as far as size 

 is concerned. It differs from them, however, in having the sculpture 

 much finer in every way. 



AGAR PANAMENSIS, new species 



Plate 1, five bottom figures 



Shell moderately large, rather inflated, white with a buffy tinge, 

 strongly rounded anteriorly, somewhat produced at the posterior 

 ventral margin. The umbones are well approximated, leaving only a 

 narrow cardinal area, which is marked by incised lines parallel to 

 the margin of the hinge. The exterior of the valves is marked by 

 strong radiating cords, of which 11 are present on the anterior part, 

 15 on the posterior part, and 39 in the middle portion. The posterior 

 part forms a decided angle where it passes into the sides. The an- 

 terior and posterior borders of the valves are rendered finely denticu- 



