40 NEW DNIONID.E OF THE 



inch in diameter. The form was frequently changed before the wound caused by 

 the knife killed the animal. It assumed that of a hemisphere, then that of a globe, 

 then again that of a stem with a round mass at the end. It evidently had the power 

 of extension into various forms at will, but the object or use of this mass in the three 

 species, in which I have alone observed it to exist, is entirely unknown to me. I 

 think it very likely that, as it is found in these three allied small species, that it will 

 be detected in others which belong to this group. All the specimens I received of 

 parvus were females and all had this caruncle like mass. I believe it belongs only to 

 the females, as in the examination of fifteen specimens o^paulus I found it to exist in 

 ten females and not in one of the remaining five males. 



Unio multiplicatus. pi. 30, fig. 105. 



Unio multiplicatus Lea, Trans. A. P. S., V. 4, new ser. pl. 4, f 2, and Obs., V. 1, p. SO. 



Unio lieros ? Say, Disseminator. 



Unio undulaius Say, Am. Conch., No. 2, pl. IG. 



Unio Jieros Say, Am. Conch., No. G. , 



Soft parts. — Branchial uterus occupies the lohole of the inner arid outer hranchice on 

 both sides. In the largest specimen of three females before me, the branchice were 

 four inches wide, one and a half long and quite a quarter of an inch thick, the whole 

 of these four masses being filled with white embryonic shells, probably to. the number 

 of three millions. Branehiai very wide, rounded behind and slightly curved below, 

 inner ones very much the larger, free or attached.* Palpi very large, oblique, thick, 

 subtriangular, united two-thirds down the posterior edges. Branchial opening very 

 large, with numerous small brownish papillae on the inner edges. Anal opening large, 

 with scarcely perceptible crenulations on the edges of some, while others seemed to be 

 entirely without. Super-anal opening very long, not united below. Color of the 

 mass whitish. The adductor muscles are enormously large and powerful, and the 

 anterior ones make corrugate cicatrices, which are deep and very rough. 



Embryonic shell is elongate, pouch-shape, slightly curved on the sides and clear 

 white.t 



Remarhs. — This is the largest species which- inhabits the waters of the United States, 

 and is remarkable for its enormous reproduction. The hrancMcd uterus pervades the 

 whole of the four leaves of the branchice, and in the largest produces three or four 

 millions of embryonic shells. This character exists only in one other species, so far as 

 I know, viz., U. ruhiginosus (nobis). (See Proc. Acad. Nat. Sci., June, 1858.) The 



*I found in the examination of five specimens of this species, that three had the branchiae attached the whole 

 length of the abdominal sack and two were free, one of them for a quarter of an inch, the other for three- 

 quarters. This is not the only instance where I have found this difference to exist. It therefore cannot make 

 a division in this family, as proposed by Prof. Agassiz, viz., those which are free and those which arc not. 



tObs., &c., Vol. 6, pl. 5, fig. 3. 



