ANODON rugosiis, 

 Wrinkled Horse Mussel. 



Generic Character. 



Testa transversa, pleru?nque temiis. Cardo linearis, edentulus. Lamina 

 cardinalis glabra, aliquando levata, antice sinu sub ligamento de- 

 sinens. Impressiones musculares 3. Ligamentum externum. Animal 

 fluviatile. 



Typus Genericus Mytilus Anutinus Lin. 



Shell transverse, generally thin. Hinge consisting of a simple mar- 

 ginal lamina without teeth, smooth or slightly raised, termi- 

 nating at the anterior end in a curve or sinus below the ligament. 

 Muscular impressions three. Ligament external. Animal flu- 

 viatile. 



Generic Type Duck Mussel Pennant. 



Specific Character. 



A. testd ovato-oblongd, crassd, cotivexd, antice oblique rotundatd ; intus 

 fulxd, margine rufo ; margine cardinali letiter curxato, infra 

 umboncs crasso. 



Shell ovate - oblong, thick, convex, anterior obliquely rounded; 

 hinge margin slightly curved and thickened beneath the 

 umbones; inside fulvous, with a reddish margin. 



iHE shells no'>v arranged under the kindred genera of Unio 

 and Aiiodon are exclusively fluviatile, or inhabitants of fresh 

 water, and are dispersed both in the old and the new world. 

 In the Linnaean system, the first, being furnished with teeth, 

 are placed among the Myce ; and the latter, from having none, 

 are arranged with the Mj/ti/i. Two common shells, in our 

 own rivers and ponds {Mt/a piclorum, and Mi/tilus anatiyius 

 Lin.), will readily present to the student the characters by 

 which they are severally distinguished. The shells of the 

 present genus bear such a general resemblance to each other, 

 and are so simple in their construction, that a corresponding 

 minuteness of discrimination is requisite to characterize the 

 species ; I have, therefore, selected for this purpose the 

 modification of the upper margin to which the ligament is 

 attached, and which in other shells forms the bases of the 



PI. 96. 



