•234 DESCRIPTION OF 



Hab. Sapotal River, near Tlocatalpam, Mexico. Dr. Burrough. 



Cabinet of Dr. Burrough. 

 Diain. .1, Length 1.4, Breadth 2.2 inches. 



Shell eUiptical, somewhat inflated, inequilateral, subbiangular behind, en- 

 larged and somewhat carinate on the umbonial slope, flattened on the umbones 

 and sub-emarginate at base; substance of the shell thick, thinner behind; beaks 

 scarcely prominent; ligament rather short and thick; epidermis yellow, the 

 whole disk being marked with green rays, darker on the posterior slope; car- 

 dinal teeth rather large, erect, single in the right and double in the left valve ; 

 lateral teeth large and nearly straight; anterior cicatrices distinct; posterior 

 cicatrices confluent; dorsal cicatrices placed in the centre of the cavity of the 

 beaks; cavity of the shell shallow; cavity of the beaks small and angular; nacre 

 somewhat golden-coloured and finely iridescent. 



Remarks. — A single specimen only is before me. Its fine rich pearly lustre 

 and beautiful iridescence are very remarkable. I have rarely seen any irides- 

 cence in a U7iio so rich. It has some resemblance to U. radiatus, and U. 

 interruptus, (nobis,) but may be distinguished from both by the flatness of the 

 umbones and the raised umbonial slope.* 



Unio Tecomatensis. Plate 21, Fig. 48. 



Testa ellipticd, inflata, in<Bquilaterali, postice suhbiangulata; valvulis crassis; natihus subprominen- 

 tihus; epidermide sitbnigrd, niiida; dentibus cardinalibus magnis; lateralibus magnis subcurvisque ; 

 margaritd vel purpurea vel salmonis colore lincld et iridescente. 



* In addition to the knowledge of the fresh water shells inhabiting the rivers and lakes of the southern 

 part of North America, so assiduously obtained by Dr. Burrough, I am indebted to another friend, Dr. 

 Blanding, for the interesting fact, that the species which I described under the names of U. Nicklinianus, 

 (see Trans., vol. 5, page 28,) and 17. discus, (see vol. 6, page 74,) inhabit the River Moctezuma, in Central 

 America, with the L''. Tampicoensis. 1 am indebted to Dr. Blanding, for specimens of these, and his 

 Cabinet may be referred to, as well as Mr. Nicklin's, and Mr. Phillips' ; these gentlemen having also 

 received specimens from Dr. B. The Nicklinianus seems always to be white in its nacre, while the discus 

 varies, some individuals being perfectly white, some rich salmon-coloured, and others of a deep purple. A 

 single valve in my Cabinet displays all these colours. 



In some of the specimens of U. Nicklinianus, there is a remarkable elevated line on the posterior slope, 

 which in some cases interrupts the folds. 



