FRESHWATER AND LAND SHELLS. 51 



On examining the peculiarity of this structure, we are led to the con- 

 clusion, that these grooves are adapted to the enlargement of the ovi- 

 ducts, and I have no hesitation in believing, that when the animal shall 

 be examined, it will be found to be adapted to this structure. In a 

 former memoir. Vol. III. p. 271, I have described the very curious 

 conformation of the oviducts of the irroratus. No species which has 

 come under my notice since, presents any thing resembling it. The 

 situation of the oviduct being about the centre of the valve, we do not 

 find that the form of the margin is changed by its sexual character. 

 The phaseolus (Hildreth) presents a very peculiar arrangement of 

 the oviducts, resembling no other species which I have examined. 

 The line of the branchiae being very long, a continued folding of 

 the whole length seems to be necessary. This is accurately repre- 

 sented in Mr Say's " American Conchology," plate 22. In the few 

 female specimens of this species which I have examined, I have not 

 been able to notice a difference of form in the shell from the male. 



The females of the U. perplexus and capssRformis, are distinguished 

 by a remarkable spreading out and extension of the whole of the pos- 

 terior part of the shell. This very naturally has been taken for a 

 deformity. 



So far as I have been able to examine the Anodontae, I have found 

 them to differ in their structure as regards the oviducts. They do not 

 appear to be divided into sacks like the U. ochraceus, cariosus, Sj-c, but 

 to present an even mass from the anterior to the posterior part. I have 

 examined numerous individuals of the two species, An. Jluviafilis* and 

 undulata (Say), which exist in our vicinity, and several Ferussaciana 

 (nobis), of the western waters which have been sent to me by my 

 brother, T. G. Lea, in a preserved state. The whole lobe of the supe- 

 rior brancMx being charged with ova, I presume that the Anodontge 

 produce more young than the Uniones. In October 1834, I examined 

 a large number of our two species from the Schuylkill, and found the 

 females very much advanced in gestation. The specimens oi Jiuvia- 

 tilis (see Plate XV. fig. 46), apparently, were ready to discharge their 

 burdens. By the pressure of the finger on the side of the oviducts, 



* Myt.fluviatilis (Soland.); An. cataracta (Say). 



