NEW FRESH WATER AiND LAND SHELLS. 233 



short time. The same inference applies to this as to circulus. Of U. occidens, 

 in column No. 4, you will see the same in March and October. 



" Few of the species in columns 1 and 2 were found with ova in the oviducts. 

 This is owing to the period at which they must be transferred from the ovarium, 

 which, most likely, is in the spring. I have observed them until the end of 

 November. After that, our river continues too high to take them until July or 

 August. In the interval the young must be perfected and discharged. By 

 reference to my notes, you will find the above facts in detail. The columns 

 are arranged and generalized from them. My observations in 1838-39 and '40, 

 are included in them, and only differ as the economy of the species itself may 

 differ. There will not be found any contradiction. 



" The ovarium constitutes much the largest portion of the body. It lies im- 

 mediately above the foot, forming all the solid part of the body between it and 

 the viscera. In a letter I sent you November 26th, 1838, were three views of 

 a U. multiplicatus, the ovarium extending from the superior part of the foot 

 nearly to the intestinal canal, and from behind and a little below the stomach 

 to the connexion of the posterior muscle, forming, with the exception of the foot, 

 the larger portion of the whole body. The integuments are thick, and on lay- 

 ing it open it has a fibrous interior with a gelatinous substance, in which are 

 disseminated numerous ova. 



" You will find in the notes sent to you in 1838 a description of both lobes of 

 the branchise on each side, of two specimens of U. multiplicatus being charged. 

 In the other specimens examined, but one lobe on each side was charged as 

 usual. In another examination, in September, 1839, both lobes were charged. 

 Thus, it appears they vary in this species, as they probably do also in TJ. ruUgi- 

 nosus.''* 



Unio Sapotalensis. Plate 21, Fio-. 47. 



Testd ellipticd, subinflata, inaquilaterali, postice suhhiangulatd ; valvulis crassis; natibus vix promi- 

 nentibus; epidermide luted, dense radiatd; dentibus cardinalibus subgrandibus ; later alibus magnis sub- 

 rectisque ; margaritd subaured et valde iridescenie. 



Shell elliptical, somewhat inflated, inequilateral, subbiangular behind ; substance of the shell thick ; beaks 

 scarcely prominent; epidermis yellow, very much radiated; cardinal teeth rather large; lateral teeth large 

 and nearly straight; nacre somewhat golden-coloured and very iridescent. 



* The 17. rubiginosus and multiplicatus, are the only species observed by my brother to be possessed 

 of oviducts, in both pairs of the iranc/jzcE. 



