U N I 



Species 505. (« ami />, ilus. D'Orbigny in IMus. 

 ]'.nt.) 



Unio Ciiarruanus. Un. testa cmssd, ventricoxd, ovali- 

 oliloagd (nouHiiiiqiiuiti obloiiyo-ehngatd) , inj'i'nie tr- 

 tiisn, post'ice o/jt/is? siibhiangulatd, aned, hnmneo-viri- 

 descente, lavigaid (nisi ad nates promintdas porcis oh- 

 Uqids subdivergentibus radiatas) ; casta umbonaU in- 

 conspicud, rotundatd ; lunula vise ttlld ; margnritd 

 argented ; dentihus cardinalibus sublamellatis. aiitico 

 in valvuld sinistra cristato vel sagrinato, postico in 

 dextrd corrugato ; lamellis laleralibus longis, rediiis- 

 cidis, e/fvotis. 



The Charrua Unio. Shell tbict, ventrieose, oval-ob- 

 long (sometimes elongated-oblong), indented below, 

 bluntly subbiangular behind, bronzed, greenish- 

 brown, smooth, except at the slightly-projecting 

 beaks, which are rayed with oblique subdivergent 

 ridges -. nmbonal ridge inconspicuous, rounded ; no 

 distinct lunule ; nacre silvery; primary teeth sub- 

 lamellar, front one of the left valve -shagreened or 

 crested, hinder of the right valve corrugated ; lateral 

 lamellae long, straightish, elevated. 



D'Orbigny, Anu'r. Merid. Moll. p. 606. pi. 71. f. S to 11. 

 U./aba, D'Orb. 



Ha!) Banda Orientale, S. America. 



The narrower form delineated is the RJnuicoiciis of 

 D'Orbigny. 



Species 506. (Mus. D'Orbigny in Mus. Brit.) 

 Unio hyl,i;us. Un. testd crassiusculd, subvcntricosd, 

 satis inceqiiilaterali, subovali, postice subbiangnlatd, 

 oUvaceo-firrugiiied vel olivaceo-lutescente,fere uudiijue 

 porcis mullis obliquis subcurvatis radiatd ; margins 

 ventrah snbretuso, aulice acclivi; costd mnbonali sub- 

 angulatd ; natibus parnis, aciUis, prominuUs ; mar- 

 garitd albidd ; dentibus cardinalibus siibtrigonis, dente 

 centrali verticali ; lamellis lateralibiis longis. 

 The eusu Unio. Shell thickish, subventricose, mode- 

 rately inequilateral, suboval, subbiangidated behind, 

 rusty or yellowish-olive, almost everywhere rayed by 

 numerous oblique somewhat cui-ved ridges ; ventral 

 edge somewhat retuse, rising in front; umboual 

 ridge subangular ; beaks small, acute, a little promi- 



nent ; nacre whitish : primary teeth subtriangular, 

 the central one vertical ; lateral lamellas long. 



D'Orbigny, Ame'r. MJrid. Moll. pi. 69. f. 8, U." 

 U. Guaraniams, D'Orb. ; do. f. 10, 11. 



Hub. Bolivia, S. America. 



An examination of the type-specimens manifests that 

 Lea is quite right in regarding the two shells as mere 

 forms of the same species. The differences are very 

 slight, and do not quite correspond to the representative 

 figures. The shell marked Guaraniana (500, «), has the 

 ridges more nodulous, a rudimentary lunule, the nacre 

 stained with olivaceous yellow in the extreme concavity, 

 and the lateral lamellse quite straight, instead of being 

 slightly curved at their extremities. There are two pri- 

 mary teeth in each valve : the ridges do not quite extend 

 to the ventral edge (especially behind), and are met at 

 acute angles beyond the ridge by a few raised lines. 



Species 507. (Mus. D'Orbigny in Mus. Brit.) 



Unio Psamjioicus. Uu. testd validd, tumidd, valde ob- 

 liqud, in senioribm valde incequilaterali, siibrhombed 

 {siiiiili t'astaliae), ferrugined vel olivaced, conceutrice 

 strils sublamellosis et radiatim porcis obliquis remotis 

 sculptd, plied umbonali angulatd; ared posticd dor- 

 suli concavd, latiuseuld, nid juxta nates valde emi- 

 nenles sitblavigatd ; lunuld distincld ; margaritd albo- 

 cixrulescente, margine cardinali lato ; dentibus cardi- 

 nalibus in utrdque valvuld 3 vel 4 ; lamellis lateralibus 

 perbrenibus, simplicibus, obliquis, subcurvatis. 



The PsAMMOic Unio. Shell strong, tumid, very ob- 

 lique, very inequilateral in the old, subrhombic, 

 (Cffs^flZifli-shaped), ferruginous or olive, with concen- 

 tric sublamellar strise, and distant oblique radiating 

 ridges; umbonal fold angular; hinder dorsal area 

 concave, rather broad, not sculptured, except near 

 the very prominent beaks ; lunule distinct ; nacre 

 bluish-white, hinge-margin broad; primary teeth 

 three or four in each valve ; lateral laraelhr very 

 short, simple, olilique, somewhat curved. 



D'Orbigny, Ame'r. Merid. Moll, p. 608. pi. 71. f 4 

 to 7. 



Eab. River Parana, Santa FJ. 



September, 1S6S. 



