394 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxx. 



N. jiucki can be readily separated from the other Nephronaias of 

 the region by its rugose sculpture, in which respect it resembles 

 N. dysoni Lea, from Costa Rica, and by its wavy radiating lines and 

 the dark nacre. 



Type.— C'At. No. 106121 U.S.N.M. The specimens were collected 

 by the Rev. W. H. Fluck at Wounta River, northwest of Kukallaya, 

 Nicaragua. 



DIPLODON HUAPENSIS, new species. 

 Plates XXVII-XXIX. 



Description. — Shell thin, elongate, elliptical, drawn out posterio- 

 ventrally into a blunt l>eak, compressed dorsally, from a line extend- 

 ing from the umbones to the posterio-dorsal margin of the ])eak and 

 somewhat pinched in its subcentral ventral half. Dorsal margin 

 slightly curved, its posterior third sloping regularh' obliquely down- 

 ward. Anterior margin abruptly' curved, falling off a little more 

 gradually toward the ventral than the dorsal edge. Posterior extrem- 

 ity evenly rounded. Ventral margin somewhat concave in the middle. 

 Periostracum brown on the posterior dorsal portions of the shell, 

 grading to wax yellow streaked with brown on the anterior ventral 

 parts. Surface marked b}' numerous lines of growth, the stronger 

 ones of which are usually darker colored than the general surface, and 

 numerous fine, crinkly, radiating lines, which. are best developed on 

 the anterior half, and gradually diminished in prominence posteriorly. 

 Beak cavities shallow. Pseudocardinals in the right valve two, nar- 

 row, weak, sublamellar, and very oblique, the dorsal one decidedly 

 notched and stronger than the ventral, which is rugose. Left pseudo- 

 cardinal narrow, slender, slight, notched, and cut into many tine 

 tubercles. Right lateral only moderately curved, very slender, 

 slightly roughened, more so on the inner than the outer edge. Left 

 laterals thin, and lamellar, inner one larger and better developed than 

 the dorsal, both with roughened edges. Nacre bluish, with many 

 spots of livid olive, which are more numerous and extensive in the 

 dorsal part of the shell than ventrall}'. Posterior part iridescent. 



There are two specimens of this species in the U. S. National 

 Museum, No. ISIUIT. The shells measure: Type, length. .5.5 mm.; 

 height, 25.9 mm.; diameter, l-i.5 mm.; the other — length, :u nun.: 

 height, 27.3 mm.; diameter, I'o mm. 



De^scrijJtion of i^oft jmrfs. — Animal pale flesh colored. Mantle 

 thickened near the edge all the way around from the anterior to the 

 posterior end; this thickening is cord-like and becomes decidedly 

 strengthened in the syphonal regions. The mantle slopes from the 

 cord to a thin edge, which is more or less marked by longitudinal, 

 parallel ridges. The space between the cord and the edge is dark col- 

 ored on the inside. Syphons completely separated, the space between 

 them being about 2 mm. wide. Ventral syphon T mm. long, thick 



