SYNOPSIS OF 



r n 



p 



-1 



Subgenus Triquetra, 1 



Having a cardinal and lateral tooth, and fur- Symphynote— Hyria corrugata. Lam. 



nished with two siphons. I 



Subgenus Prisodon, 2 f M c , , ~ , v , . 



° JNon-bymphynote — Castaha ambigua. 



Having a cardinal and lateral tooth transversely \ j 



striate, and furnished with two siphons. I 



Subgenus Unio, 



Having a cardinal and lateral tooth. 



Subgenus Margaritana, 

 Having one tooth (cardinal). 



Subgenus Monocondyloea, 



Having a simple callus. 



Subgenus Dipsas, 



Having a linear tooth under the dorsal margin. 



Subgenus Anodonta, 3 

 Having no teeth. 



I Symphynote — Unio alatus. Say. 



I Non-Symphynote — U. pictorum. Lam. 



j Symphynote — Alas, complanata. Barnes. 

 [ Non-Symphynote — Alas, undulata. Say. 



j Non-Symphynote — Mono. Paraguayan a. 

 { U Orb. 



-j Symphynote — Dipsas plicatus. Leach. 



\ Symphynote — Sym. magnifica. Lea. 

 j Non-Symphynote — An. fluviatilis. Lea. 



1. 



Subgenus Iridina, 



Having a granulate dorsal margin, and furnished Non-Symphynote— I. exotica. Lam. 

 with two siphons. [_ 



2. Subgenus Spatha, f 



Having a dorsal margin non-crenulate, and fur- Non-Symphynote— I. rubens. Desk. 

 nished with two siphons. [ 



3. Subgenus Mycetopus, r Non _ symphynote _Myc. soleniformis. 



Having a straight, smooth, dorsal margin, and 1 JJ Orb. 

 furnished with a long extensile foot. [ 



1 Since the publication of the last edition of this Synopsis, the soft parts of Triquetra (Hyria, Lam.) have been 

 obtained, and Mr. Gray, in the An. and Mag. N~at. Hist., vol. vi., gives us the anatomy. "The mantle lobes of 

 the species of this genus brought from British Guiana by Mr. Schomburgh are united together behind, and furnished 

 with two short, separate, contractile siphons, like the animals of Iridina and Leila, though the submarginal impres- 

 sion of the shell does not show indications of any inflections behind." 



3 M. D. Orbigny, in his Voy. Am. Mer., vol. v. p. 597, gives a description of the soft parts of Prisodon (Cas- 

 talia, Lam.). Mantle open the whole length, except at the anal region, where it is closed, and presents two short 

 distinct tubes, of which one — branchial — is largest and furnished with cilise round its edge. Buccal appendages 

 rounded, very large. Foot much compressed, thicker and bent behind. 



3 A very remarkable fresh-water bivalve, named Byssanodonta Paranensis by D'Orbigny, was observed by him 



