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v 
514 MOLLUSCA. 
42. Unio cognatus. 
Unio cognatus, Lea, Proc. Acad. Phil. 1860, p. 306°; Journ. Acad. Phil. (2) iv. p. 368, t. 65. 
fig. 193°; Obs. Gen. Unio, viii. p. 50, t. 65. fig. 193°; Fisch. & Crosse, Miss. Scient. Mex., 
Moll. ii. p. 662 *. 
Oval, rather thick and swollen, yellowish-green, with dark rays ; cardinal teeth strong. 
Hab. N.E. Mexico: Rio Salado, State of Nuevo Leon (Berlandier }~*). 
Allied to the North-American U. venustus and U. zigzag. 
IX. Exuiprio, Raf. 
43. Unio rubicundus, sp. n. (Tab. XXXIV. figg. 3, 3a.) 
Testa oblonga, trapezoidea, concentrice grosse striata, striis nonnullis subnodulosis, in declivitate posteriore 
pliculis numerosis obliquis sursum arcuatis sculpta, rufo-fusca, parte antica longiuscule rotundata, parte 
postica declivi-rostrata et subperpendiculariter truncata, linea angulari a verticibus descendente, margine 
ventrali antice valde ascendente, medio et postico recto; dentes cardinales validi, triangulares, sulcati et 
crenulati; facies interna purpurea, linea palliali antice a margine valde remota. 
Long. 89; alt. vert. 57, ale 44, diam. 34 millim. Vertices in 3 long. 
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| Hab. N. Guatemata: Coban (Conradt). 
Although a single valve only of this species has been obtained, I am compelled to 
propose a new name for it. In size and outlines U. rubicundus so nearly resembles 
U. corium, Sowerby, that, at first sight, it seemed to be nothing more than a smooth 
variety of that species; the sculpture, however, is different: this is due to the presence 
of coarse concentric strie, some of those on the umbonal region rising here and there 
into flat prominences, but the summits themselves (which, fortunately, are well 
preserved) are simply concentrically striated ; there is no trace of granulated structure. 
On the hinder slope there are small plaits, bent upwards, as in U. pliciferus. The 
cardinal teeth are rather strong. The sculpture is unlike that of the species of the 
subgenus Psoronaias, and, as placed here, near U. pliciferus, in the subgenus Lilliptio, 
U. rubicundus differs from all its allies in the large size and thickness of the shell and 
in the stout teeth. 
Unio rugoso-sulcatus, Lea, Obs. Gen. Unio, xii. p. 26, t. 34. tig. 81 (1866), supposed 
to be from Central America, is rather near the present species, but it is a little more 
triangular, without prominences and plaits, and has the hinder part distinctly 
biangulated. 
44, Unio pliciferus. 
Unio pliciferus, Lea, Trans. Am. Phil. Soc. vi. p. 61, t. 17. fig. 53 (1836)*; Obs. Gen. Unio, ii. 
p. 61, t. 17. fig. 53°; Hanley, Cat. Rec. Bivalv. p. 176, t. 20. fig. 32°; Kiister, in Martini 
& Chemnitz, Syst. Conch.-Cab., ed. 2, Unio, p. 142, t. 42. fig. 1*; Chenu, Manuel de 
Conch. ii. p. 142, fig. 702°; Sowerby, in Reeve’s Conch. Icon. xvi., Unio, t. 75. fig. 887°; 
Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 580, t. 65. fig. 2, and t. 70. figg. 2, 2a". 
