﻿220 new unionim: of the 



cardinal tooth a broad arched plate ; anterior cicatrices distinct and deeply impressed ; 

 posterior cicatrices distinct and deeply impressed ; dorsal cicatrices placed under the 

 plate, above the centre of the cavity of the beaks ; cavity of the shell moderately 

 deep and rounded ; cavity of the beaks shallow and very obtusely angular ; nacre 

 white and iridescent. 



Remarks. — Several of this interesting little species are before me. It is to be 

 regretted that none were collected with the soft parts for examination. It is closely 

 allied to nucleopsis Con. and Trocheliamis (nobis) ; but it is more rotund in its outline, 

 and, indeed, more orbicular than either of them. The lines of growth are very 

 regular, nearly equidistant and in the adult number about a dozen. The lateral teeth 

 are very robust, that of the right valve being so much thickened as to approach to 

 duplication. The angle between the cardinal and lateral teeth is unusually small, 

 the older specimens being about 50°, while in the younger ones it is nearly 60°. None 

 had perfect beaks, so that the character of the undulations might be observed, but I 

 have no doubt the tips will be found to have two or three rugose undulations. 



Unio phaseolus Hild.* PI. 29, fig. 101 and 101 a. 



Soft parts. — Branchial uterus occupies the whole length of the outer branchiae, and 

 the upper pointed end of the branchial ovisacks is inserted about one-fourth of an 

 inch from the upper margin in a zig-zag line. These sacks are so numerous, and 

 enlarging as they do, by their clavate form, at the lower end, that they necessarily 

 fall into a succession of folds. In the specimen here described and figured there are 

 thirty-eight folds on each of the outer leaves of the branchice. These folds will average 

 half an inch, which really gives the length of the line of the lower border nineteen 

 inches, while the shell itself is but three and one-half inches wide. The form of the 

 branchial sackf (pi .29, fig. 101 a) is that of a very much elongated cone, and its colored 

 margins are altogether very peculiar. From the apex towards the base it is purplish 

 brown, and this gives the whole mass above a dark hue ; but where this ceases near 

 the base, there is a dark brown spot on each side surrounded below by a fine brown 

 line, presenting the appearance of a festoon. Below this at the terminal point of each 

 branchial ovisack there is a bright red spot, which gives to the whole mass, seen from 

 below, the appearance of rows of minute red currants or beads. The folds are longer 

 in the middle and shorter towards the end of the branchiae. Branchice, the inner ones 

 are very large, coming much below the charged branchial leaf of the outer ones, and 

 are united about half the length of the abdominal sack. Palpi subtriangular, rather 

 large, thin, united one-third down the posterior edges. Mantle very thin, thickened 

 along the margin, which is slightly colored. Branchial opening with very small brown 



*Am. Journ. Sci., Vol. 14. 



fFig. I, a, represents three of these sacks placed contiguously to show their form and markings. 



