tl.VITKI) STATES AND XOKTIIF.r.N .MKXICO. 45 



beaks; cavity of the shell deep and wide; cavity of the l)e:iks very shallow and 

 subangular ; nacre bluish white and iridescent. 



Soft Parti. — Branchial titerus filled the whole length of tiie outer hranciiia; very 

 much like flariatilis. Branchio' rather large, rounded below, inner one much tho 

 larger, free two thirds the length of the abdominal sack. Paljn not large, .subtri- 

 angular, united a short distance on the posterior edges. Mantle thin, transparent, 

 thickened at the edges, and colored blackish and brown at syphonal openings. 

 Branchial opening with rather delicate and slender papillic, which are light brown 

 and yellowish, surrounded with a black pigment. Anal oimiing small, nuiculate with 

 light brown, and black within the edges, the edges being black. SujKr-unal opening 

 rather large, distant from anal opening, slightly colored on the edges and united below 

 for some distance. Color of the mass whitish, in some cases a little salmon colored. 



Enthryonic shell light brown, triangular, with hooks.* 



Out of 40 opened in April only three had any living young in the branchial uterus. 

 They remained in the anterior part of the outer branchise. In a few dajs theise 

 would have been discharged. It is evident, however, that the whole length of the 

 outer branchise had been charged as in fluviatilis. On examination of the ovaria, I 

 found several females with incipient ova, but nearly all which were examined proved 

 to be males. 



Remarks. — Among the hu-ge number of fine fresh water shells sent to me by my 

 friend Dr. Lewis from time to time, were living specimens of all ages of this species, 

 which had not been before noticed, and it is with j)eculiar pleasure that I have dedi- 

 cated it to one who has done so much and so judiciously in this branch of Malacology 

 in his own State. This species is closely allied to fiuviatilis, Sol., as it is also to 

 lactistrls herein described. It differs from the first in the form of the undulations of the 

 beaks as well as in the color of the epidermis, it being very much darker. It differs from 

 lacifiilris in being darker and not banded and in having rugose, granular indications on 

 the tips. It is also more swollen about the middle of the disk than either of these 

 species. 



Anodonta lacustris. pi. 62, fig. 188. 



Testa lacvi, transversa, subinflata, valdo inaequilaterali, posticc subangulata; valvulis tcouibus; natibus 

 prominulis, ad apices crebri undulatis; epiderinide luteo-olivacea, vel eradiata vol obsolete radiata 

 transversi vittata; margarita vel alba vel crocea et iridescentc. 



Shell smooth, transverse, somewhat inflated, very inequilateral, subangular behind; 

 valves thin ; beaks slightly prominent, closely undulate at the tips ; epidermis yellow- 

 ish olive, eradiate or obsoletely radiate, transversely banded ; nacre white or reddish 

 brown and iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 84. 



*Sof (Icscriplion and figure. .lour. Acad. Nat. Sci. vnl. iv. p. i;>. and 01l^■. on Unio, vol. vi. p. 49. 



