2 1 8 



more in< pearly white. U. Menkeanvs is mon 



tip more acute, tooth in left valve deep cleft. 



I'md petrintjs. T. solida, ovato-quadrata, subeqnilateralis, an- 

 tice acute rotundata, postice late truncata, subtua vix arcuata, prope 

 marginem dorsalem posticum plicis obliquis minimis ornata; umboni- 

 bus modicis, subplanulatis ; epidermide dilute flavo-viridi; dentibus 

 cardinalibus robustis, pyramidatis, Iateralibns curtis ; margarita alba. 

 Long. l£; alt. I- 1 -; lat. | poll. Llanos River, Texas. Dr. T. H. 

 Webb. 



May be compared to U. Lamarckianus, Lea, (=U. Aberti, Conr.) 

 ll is less compressed, apices less acute, and less angular ; the posterior 

 altitude is greater, the posterior dorsal margin being less declivous, 

 but as the posterior truncation is less decided, the length is greater 

 compared with the height; the surface is irregular, but destitute of 

 granules or nodules. 



Unio mantjbitjs. T. transversa, elongata, subarcuata, subven- 

 tricosa, antice angustata, postice acuta, margine dorsali arcuato 

 in marginem posticum desinente; disco rudi, epidermide nitido-corneo 

 induto ; dentibus cardinalibus compressis, triangularibus, ad margi- 

 nem fere parallelis : d. Iateralibns remotis, arcuatis ; margarita argen- 

 dcosa. Long. 3|; alt. 1 g ; lat. I- 1 - poll. Chihuahua, sixty miles 

 from Camp Ringgold. ' By Dr. T. II. Webb. 



Allied to U. declivis, Say =gt < Lea. in which the posterior 



extremity is recurved and angular, rather than decurved with round- 

 ed angles ; and the surface is dead and dusky. In our shell, the 

 anterior extremity is more prolonged, and much more slender. It is 

 also intermediate between U. obesus, Lea, and U. camptodon, Say. 



Anodon iiorda. T. tenuis, transversa, elongato-ovata, ventri- 

 dilute cornea, viridi nubeculata, antice angustata, subacuta, 

 postice subtruncata, dorso excavato, declivitate umbonali obtuse 

 angulato, submarginato, umbonibus obtusissimis, pallidis, tenuiter 

 undulatis, ad trientem anteriorem sitis; margarita argentea. Long. 

 3£; lat. 1^; alt. 1| poll. Comanche Creek, Texas. Dr. T. H. 

 Webb. 



Remarkable for the broad, inflated, pale beaks, presenting no dis- 

 tinct apex. In size and form, it might, at first sight, be taken for U. 

 anodontoid.es. It approaches to A. ferruginea and A. Dunlapiana, 

 but differs in its proportions. 



Cyclas nobilis. T. magna, solida, ovato-rhomboidea, utrinque 

 truncata sed postice obliquius ; umbonibus anticis, tumidis; margine 

 dorsali utrinque arcuatim declivibus; margine ventrali arcuato; val- 

 vis remote et profunde sulcatis; epidermide flavescente ; dentibus 

 cardinalibus minimis; intus pallida. Long. \ ; lat. ', : alt. | poll 

 Found near San Pedro, California. Dr. Webb. 



