Art. 11 NEW AMERICAN MAKINE MOLLUSKS BARTSCH 29 



This species differs from the two previously known forms, Artiphi- 

 thalamus inclusus Carpenter and Amphithalamus tenuis Bartsch in 

 being much stouter than A. tenuis Bartsch, and in having coarser 

 spiral threads on the early whorls, a less strong peripheral keel, and 

 more rounded whorls than A. inclusus Carpenter. 



ALVANEA SANJUANENSIS, new species 



Plate 3, fig. 7 



Shell moderately large, chestnut brown excepting the tip, which 

 is a little paler and the extreme base which is lighter. Nuclear whorls 

 one and a half, well rounded; the sculpture of the nuclear whorls 

 eroded in all the shells seen except in a very small fraction of the 

 last turn in the type, which presents a finely, somewhat wavy, spir- 

 ally lirate surface. I am not quite certain whether axial threads are 

 present or not. Postnuclear whorls strongly shouldered at the sum- 

 mit, strongly rounded, marked on the first turn by three strong 

 spiral cords, which occupy the anterior half of the turn ; on the 

 second turn a fourth cord occurs a little anterior to the median line 

 between the summit and the first strong cord, while on the next 

 turn a fifth slender thread makes its appearance between the summit 

 and this cord. This last cord at the summit never attains a strength 

 as great as the third anterior to it, while the second one is fully as 

 strong on the penultimate turn. In addition to these spiral cords 

 the shell is marked by rather weak axial ribs, of which 24 occur 

 upon the second, 26 upon the third, and about 32 upon the last turn ; 

 on this they are decidedly enfeebled. The junction of the axial 

 ribs and spiral cords forms feeble nodules. The entire surface of 

 the spire between ribs and interspaces is crossed by fine spiral and 

 axial threads which lend it a fine clothlike texture. Suture strongly 

 constricted. Periphery of the last whorl well rounded. Base mod- 

 erately long, well rounded, marked by seven equallj'^ spaced spiral 

 threads, of which the seventh immediately behind the inner lip is 

 very feeble. The rest are almost as wide as the spaces that separate 

 them. The axial ribs do not extend over the base, but the fine sculp- 

 ture described for the spire is also present here. Aperture ovate; 

 posterior angle obtuse; outer lip thin at the edge, strongly curved; 

 inner lip strongly curved, reflected and appressed to the base except 

 at the extreme tip ; parietal wall covered by a thick callus, which 

 renders the peritreme complete. 



The type. Cat. No. 334487, U.S.N.M., was collected by Dr. C. C. 

 Engberg at San Juan Island, Gulf of Georgia. It has five whorls 

 and measures, altitude, 3 mm. ; diameter, 1.5 mm. Three additional 

 specimens. Cat. No. 363777, U.S.N.M., come from the same gathering. 



