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TRIAITGULAE. 



J/j/a plana. Eat. 

 Mya gracilis. Eat. 

 Iletaj^tera gracilis. Stiinpson. (Agass. 

 MSS.) 



OVAL. 



*geiierosus. GoulcU Blan. 



OBLONG. 



*pressus.' Lea. 



Symph. compressa. Lea. 

 Complanaria alasmodontina.^ Stimp- 



$011. (Agass. MSS.) 

 TJnio compressus. Con. Adams.* 

 Linsley. Dekay. Han. 



*decoratus. Lea. 



QUADRATE. 



*atTomarginatus. Lea. Chenu. 



*imiltiplicatus.' Lea. Kirt. Potier. 

 Chenu. Han. 

 Unio heros. Say, in Disseminator. 

 Unio undulatus. Say, Am. Conch. 

 No. 2, PL 16, Deshayes. 



\ 



QUADRATE. 



Unio heros 



Con. 

 Unio atrocostatus 



Say, Am. Concli. No. 6. 

 Beeve, No. 13. 



*Eiglitsii. Lea. 



*Neislerii. Lea. 



*undulatus. Ear. Valen. Hild. Desh. 

 Chenu. Han. 

 Unio eostata? Baf. 

 Unio costaius. Con. 

 Unio plicatus. Con. 

 Mya undulata. Eat. 



*perplicatus. Con. 



Unio Pearlensis. Con. 



*atrocostatus. Lea. 



*Elliottii. Lea. 



1 Dr. Gonlcl (Boston Nat. Hist. Soc, April, 1847) says it resembles Margaritana Vondemhushiana, 

 Lea, now transferred to Monocondylcea, D'Orb. 



2 In the Proceedings of the Am. Phil. Soc, vol. ii. p. 237, I changed compressus into pressus, the 

 former name having been used by Sowerby for a fossil sf»ecies. 



^ Where did Barnes describe '■'■Unio Alasmodontinus, Barnes," as quoted by Agassiz? 



* '•^Fresh ivater and land shells of Vermont." His variety plebeius does not seem to me to differ. 

 My brother, T. Gr. Lea, stated to me that he thought the U. pressus properly belonged to the genus 3Iar- 

 garitana, and that the charged ovisacs were like those of 31. complanata. In all the fifteen which he 

 found during several years, the ovisacs were charged. I have since examined a female, and find this 

 species has in the soft parts other characters like Margaritana, but not completely so, and ha-vdng true 

 lateral teeth, it must be placed with Unio. 



^ When I described the multiplicatus in 1830, 1 had had several specimens for two or three years, 

 and was not aware that Mr. Say had published a shell under the name of heros, which he subsequently 

 abandoned as the undulatus of Barnes; but in 1834 reclaimed as heros. The figure of Mr. Say in Ame- 

 rican Conch., pi. 16, is certainly not U. undulatus, Bar., as he supposed. It is undoubtedly my multipli- 

 catus, as a comparison of the two figures will prove. Mr. Say refers to Barnes's fig., Am. Jl. of Science, 

 vol. vi. pi. 2, as being the same with this ; but a comparison will show that they are not alike in outline, 

 in folds, nor in the beaks. 



