NEW EXOTIC UNIONIDiE. 379 



Diana. -S, Length 2-6, Breadth 2-9 inches. 



Shell smooth, nearly round, very much compressed, inequilateral, rounded before 

 and behind ; substance of the shell thick, thicker before, with a very broad, thick 

 basal margin ; beaks somewhat prominent and compressed ; ligament short, rather 

 thick and dark-brown ; umbonial slope scarcely raised and rounded ; posterior slope 

 compressed and raised into a carina; cardinal teeth rather small, rather compressed, 

 divided into three lobes in the right valve and crenulate ; lateral teeth rather long, 

 very much curved, forming an arch at the plate posterior to the cardinal teeth ; 

 anterior cicatrices rather small, well impressed, confluent with the lower but distinct 

 from the upper; posterior cicatrices rather large, confluent and very slightly im- 

 pressed ; dorsal cicatrices well impressed, and placed within the cavity of the beaks ; 

 cavity of the shell very shallow and wide ; cavity of the beaks very shallow and 

 subangular ; nacre white or salmon color. 



Remarlcs. — This is a very remarkable species, being exceedingly compressed and 

 nearly round. Its thick, black epidermis is very uncommon, and this thickness 

 causes it to peel off in flakes. The form of the cardinal teeth is very unusual, being 

 treble in both valves, while the lateral tooth has the normal character of the Unto 

 in being double in the left and single in the right valve. The great thickness and 

 width of the basal margin below the palleal cicatrix is very striking. It exceeds 

 Paranensis (nobis) in that respect, while it has other characters closely in relation. 

 The rotundity is nearly the same, but it differs in the teeth, in the color of the 

 epidermis and in being more compressed. It belongs, of course, to the group of 

 which Paranensis may be considered the type. In the two specimens before me 

 both have the beaks much eroded, and therefore the character of the tips cannot 

 be given ; but I have no doubt this will be found to have radiate undulations. One 

 of the specimens has a white nacre, the other is slightly salmon color. The interior 

 of the cavity, from the palleal cicatrix, in both specimens, is covered with epider- 

 mal layers, giving a greenish hue to nearly the whole surface. 



Unio piceus. PI. 41, fig. 287. 



Testa lasvi, clliptica, subinflata, valde inaequilaterali, postice subrotundata, antice oblique rotundata; 

 valvulis crassiusculis, antice aliquanto crassioribus ; uatibus proniinulis; epidermide micante, nigra,, 

 striata, obsolete radiata vel eradiata; dentibus cardinalibus parviusculis, compressis, obliquis, in 

 valvulo sinistra singulis ; lateralibus sublongis subcurvisque ; margarita caeruleii alba et iridescente. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, somewhat rounded 

 behind and obliquely rounded before ; valves somewhat thick, slightly thicker 

 before; beaks slightly prominent; epidermis shining, black, striate and obscurely 

 rayed, or without rays ; cardinal teeth rather small, compressed, oblique, single in 

 the left valve ; lateral teeth rather long and somewhat curved ; nacre bluish white 

 and iridescent. 



