1890.] 



NATURAL SCIENCES OF I'HILADELPHIA 



283 



The dentition is like albohibrls except that the side cutting- 

 points of the central 

 and inner lateral teeth 

 are less developed than 

 Binney's figures show. 

 There is considerable 

 variation in this char- 

 acter, however, in tiie 

 real (dbolabris. 



The genitalia show 

 the affinities of the specimens more plainly than the shells, having 

 the spermatheca or receptaculum seminis (r. s.) exactiv as in Leidv's 



figures (Terr. Moll. I.). Its 

 prominent character is in the 

 greatly swollen base of the 

 duct (b.), which is found in 

 no other Mesodon, but which 

 the observations of Dr. Leidy, 

 W. G. Binney and my own 

 numerous dissections prove 

 to be a constant and very 

 obvious specific character of 

 albolabris. The penis-sack 

 (/).) is swollen in the middle, 

 as in albolabris. The vas 

 X-^- deferens is as in albolabris 

 exce])t that it is much shorter, 

 not being thrown into a knot 

 or mesh of convolutions be- 

 fore it enters the penis as it 

 is in true albolabris. This 

 last character is an import- 

 ant one. The bundles of 

 coecfe of the ovotestis are 

 shaped like those figured by 

 Dr. Leidy for H. thyroid es. 



The specimens were collected in August of this year. 



Mr. Charles P. Perot was elected a member of the Finance Com- 

 mittee to fill the vacancy caused by the election of ^Nfr. Isaac C. 

 Martindale to the Treasurership. 



The following were ordered to be printed : — 



