R2 DESCKIPTIONS OF 



having two marks of growth, one at the margin and the other about half way. In 

 the nacre the two differ, one being golden yellow and the other purplish, inclining to 

 pale pink. The nacre is thicker and shows a band or thickening inside where the 

 marks of growth exist outside. One of the valves is flatter on the middle and more 

 suddenly compressed on the anterior portion than the others, and they are both 

 slightly darker on this anterior portion. There is a disposition on the middle of both 

 valves to be wrinkled ; the impressed lines being very irregular. The undulations 

 of the tips are very minute, irregular and very beautiful. This species can not be 

 compared with any of the Monocondylcea I have seen. Its peculiar rhombic form 

 places it in a division peculiar to itself. 



Unio bulloides. pi. 42, fig. 144. 



Testa sulcata, subrotunda, valde ventricosa, subsequilaterali, postice subalata, antice rotundata ; valvulis 

 subtenuibus ; natibus prominentibus, tumidis, ad apices radiis elevatis divaricatis ; epidermide luteo- 

 fusca, crebris transversis sulcis, eradiata. ; dentibus ^ardinalibus prselongis, lamellatis, vald^ obliquis ; 

 lateralibus sublongis, lamellatis subrectisque ; margarita alba et iridescente. 



Shell sulcate, rounded, very much inflated, nearly equilateral, somewhat winged 

 behind, rounded before ; valves rather thin ; beaks rather prominent, swollen, with 

 divergent raised rays at the tips; epidermis yellowish "brown, with close transverse 

 furrows, without rays ; cardinal teeth very long, lamellar and very oblique ; lateral 

 teeth rather long, lamellar and nearly straight ; nacre white and iridescent. 

 Unio bulloides, Lea. Proc. Acad. Nat. Sci., 1859, p. 1S7. 



Hah.— Rio de la Plata, South America. G. Von dem Busch, M. D. 



My cabinet and cabinet of Dr. Von dem Busch, Bremen. 

 Diam. 1-2, Length 1-6, Breadth 1-9 inch. 



Shell sulcate, rounded, very much inflated, nearly equilateral, somewhat winged 

 behind, rounded before ; substance of the shell rather thin ; beaks rather prominent, 

 swollen, with numerous rather small, divergent raised rays at the tips; ligament 

 short and rather thick; epidermis yellowish brown, with close transverse furrows, 

 without rays, with indistinct, distant marks of growth ; umbonial slope raised and 

 rounded ; posterior slope wide ; cardinal teeth very long, lamellar, very oblique and 

 single in the left and double in the right valve ; lateral teeth rather long, lamellar 

 and nearly straight; anterior cicatrices confluent, not very large and slightly im- 

 pressed ; posterior cicatrices confluent and very slightly impressed ; dorsal cicatrices 

 well impressed, in a row across the centre of the cavity of the beaks ; cavity of the 

 shell deep and rounded ; cavity of the beaks rather deep and subangular ; nacre 

 white and iridescent. 



Remarks. — A single specimen of this very much inflated species was sent to me by 

 Dr. Von dem Busch. The epidermis is a good deal eroded towards the beaks, but there 

 seems not to have been any rays. The marks of growth are indistinct and somewhat 



