THE FAMILY NAIADES. 



27 



2 

 < 

 a 

 Pi 



< 



H 

 O 



12; 

 t- 

 K 



z 



o 



QUADRATE. 



*confiagosa. Lea. 

 Alas. coLifragosa. 



TRIANGULAR. 



*aicula. Lea. 



Say. 



OBLONG. 



*marginata. Left. 



Alas, maigiiiata. Say. Bar. 



Alas, truncala.f Say. 



Unio cariosa. (Var. 2.) Lam. 



Unio varicosa. La)?i. 



Unio calceolus. Say, not of Lea. 



Mya regulosa. Wood. 



*rugosa. Lea. 



Alas, rugosa. Bar. Eat. Hild. 

 Alas, abdiicla. Say. 



TRIANGULAR. 



*cleltoidea. Lea. 



*unclulata. Lea. 



Alas. undula(a. Say. Bar. 

 Alas, sculptilis (young). Say. 



o 



3 



P-i 



TRIANGULAR. 



Mya undulala. Wood. 

 Unio liians. Valen. 

 Unio glabraUis. /Soic. 



OVAL. 



*Raveneliana. Lea. 



radiata.| Lea. 



Alas, radiata. Con. 



*calceola.§ Lea. 



Unio calceolus. Lea, Trans. Am. 



P. S. 

 Alas. niarginata.|l Say. 

 Alas, tiuncata. Con., not of Say. 



OBOVATE. 



*Bonel!ii. Lea. 



Alas. Bonellii. Fer. 



Unio depiessa. P/e?/. Mithl. 



Unio conipiessa. Menke. 



*Paraguayana. Lea. 



Monocondylffia. Paraguayana.^ 



L L 



D'Orb. 



t Several specimens of fine marginata have been sent to me from the west, marked Alas, truncata, Say, being 

 one of his unpublished names, but given by him to various conchologists under that name. I have never consi- 

 dered it distinct from the marginata of the eastern rivers, although it is generally larger and of finer colour in 

 the exterior. 



X This shell, in the teeth, except in the size of them, very closely resembles the An. areolatiis, Swain, 

 which Mr Say described as Alas, edentula. Although in both these shells there is a small cardinal tooth, in all 

 their other characters they so closely resemble the Anodontx, that it is a matter of doubt with me as to the pro- 

 priety of separating them. An examination of the animals, when satisfactorily dissected, may show the ne- 

 cessity of placing them both, notwithstanding their possessing small teeth, with the Anodontx. 



§ In my Memoir in the Trans. Am. Phil. Soc, Vol. III. page 420, (page 34 of " Observations on the Genus 

 Unio,") I mention tins shell as being closely allied to the genus Alasmodonla of Say. In this Synopsis I have 

 deemed it belter to transfer it to the subgenus Margarilana, as the lateral tooth is observable in very few indi- 

 viduals. Deshayes says it is between Unio and Alasmodonta. 



|] Mr Say in his " Synonymy" makes calceolus and Alas, marginata the same. I am surprised at this, as 

 their characters, in many respects, are very diflerent, and I have never heard it even suggested before that they 

 could b*e confounded. 



If D'Orbigny, the distinguished traveller in South America, forms the genus Monocondylaa for a group of 

 shells which he has first observed, and which possess a single cardinal tooth. This tooth certainly differs from 

 that of the Margaritana JluviatiUs, Schum., Alasmodonta, Say ; but for the present, at least, I prefer placing 

 them in Schumacher's genus. The possession of one cardinal tooth, and the absence of a lateral one, is the dis- 

 tinguishing character of both of them. I am indebted to the great kindness ofM. D'Orbigny for the first five — 



