THE NAUTILUS. 87 



with small pustules arranged in upcurved lines. Epidermis 

 yellow, horn color, sometimes obsoletely rayed, on the posterior slope. 

 The shell would seem to be nearly smooth, but in all the specimens 

 seen there are numerous irregular, radial, pit-like impressions and 

 concentric striae, and shallow sulci. The radial impressions or pits, 

 extend through the shell, and are visible inside and out. HiiiLT^ 

 ligament, stout and rather long. Muscle scars well marked, separate 

 in front, confluent behind. Teeth stout, double in the left, and 

 single in the right valve. Beak cavities shallow, with a row of 

 muscle scars running downward, forward and onto the base of the 

 cardinal tooth. Nacre white, flesh color or dark purple, very 

 irregularly laid on, and very thin. Except in old shells, the pris- 

 matic structure extends far beyond the nacre, and the epidermal 

 layer, in turn, extends still further. 



Length 80, height 47, diameter 25 mm. 



Habitat: Valles River. — Collected by Mr. A. A. HlNKLET. 



A cotype in coll. A. N. S. Phila., measures, length 81, height 51, 

 diam. 22 mm. 



The shell is not related very closely to any species that I know of. 

 In fact I am undetermined whether to place it in Lampsilis or in 

 Nephronaias. In the absence of any data regarding the animal, it 

 is provisionally placed in Lampsilis. Mr. Hinkley informs me that 

 it is near to, if not identical with an undescribed species labeled by 

 Mr. Chas. F. Simpson as Lampsilis sali?iasensis, which however Mr. 

 Simpson has not described, and which he informed me, he does not 

 intend doing. 



The prismatic layer is A- inch wide at the edge in some cases. 

 This peculiarity accounts for the pitting, and numerous irregular 

 sulcations being, it is evident not normal, but the result of numer- 

 ous accidents which befall the extremely delicate edge of the shell. 



Plate 12, two upper figures represent the type specimen ; lower 

 left-hand figure is a young shell. 



THE GRAVID PERIODS OF TJNIOS. 



BY CHARLES H. CONNER. 



About four years ago, I began to collect systematically data rela- 

 tive to the gravid periods of Unios. Some of the results are pre- 

 sented herewith, in the hope that they will be of interest. 



