ly NEW DNIONID^E OF THE 



lamellar and nearly straight; anterior cicatrices distinct and well impressed ; posterior 

 cicatrices confluent and slightly impressed; dorsal cicatrices placed under the plate 

 above the centre of the cavity of the beaks ; cavity of the shell shallow and wide ; 

 cavity of the beaks shallow and rounded; nacre white, purple or salmon and very 

 iridescent. 



Soft Parts. — Branchial uterus occupying, like complanatus, the whole width of the 

 outer branchijB, which were filled with ova, but none were matured ; ova were found 

 also in the ovarium. Brancliioi wide, oblique behind and rounded before, inner ones 

 much the larger. Palpi thin, subtriangular, united one-fourth down the posterior 

 edges. Ma7itle thin, thickened at the margin, obtusely angular behind. Branchial 

 opening rather large, with small brown papilla3. Anal opening rather large, with 

 numerous small brown papillse. Super-anal opening very long and united below. 

 Color of the mass light salmon. 



Remarhs. — I have about a dozen of this species before me, three of whicii are 

 females in alcohol. It is of the complanatus group, but is more quadrate, thinner 

 and smaller than that species. There is one very unusual character about these 

 specimens, but it may not be permanently characteristic, as I have seen it occasionally 

 in other species, though rarely. I mean the sudden constriction at the second line of 

 growth about the middle of the disk, which forms a kind of hip there and gives the 

 upper portion an inflated form. Above this line the disk is smooth, usually brown, 

 sometimes yellowish, and obscurely rayed, while below it is without rays and usually 

 transversely banded with yellow and brown. The stricture about the middle of the 

 disk is always apparent inside, as the plane of the nacre is interrupted by it. In two 

 of the specimens there is a well impressed ventral cicatrix in each valve. In a single 

 specimen the beaks are nearly perfect, and the fine undulations are sufficiently so to 

 'be characterized. They are much like those of complanatus, being transverse on the . 

 side and angular on the umbonial slope. From the appearance of all the specimens I 

 suspect that, when young, that is before they have arrived at the age of constriction, 

 the disks are all yellow and nearly covered with fine green rays. On all the 

 specimens received there was more or less red oxide of iron, which obscured the epider- 

 mis and was difficult to remove. 



Unio latus. pi. 53, fig. 159. 



Tests, Icevi, transversa, cotnpressfi, postici obtuse angulattl, valde inrequilaterali ; valvulis subtenuibus ; nati- 



bus prominulis; epiderniide luteola vel luteo-fusca, niicante et perradiata; dontibus cardinalibus parvis, 



subcompressis, striatis ; lateralibus prslongis, lamellatis subreetisque ; luargarita vel albii vel purpuras- 



cente vel salmonis colore tincta et valde iridescente. 



Shell smooth, transverse, compressed, obtusely angular behind, very inequilateral; 



valves rather thin; beaks slightly prominent; epidermis yellowish or yellowish 



brown, shining and rayed all over; cardinal teeth small, rather compressed and 



