CONRAD'S NEW SPECIES OF UNIO. 297 



The name of imrallelus having been previously given by Sowerby to a fossil species, 

 to prevent confusion another name has been substituted. 



U. ARQUATUS. PI. 26, fig. 8. — Oblong, moderately thick before, tbinncr behind; hinge ami b:isal margins 

 pirallel; basal margin contvacteJ ; nmbonal slope ventricosc j posterior margin very obliquely truncateJ ; 

 extremity obtusely rounded; epidermis olive-yellow, with dark green rays over the whole disk; within 

 white; cardinal teelh robust ; one direct tooth obliquely striated in the right valve, and two teeth ia 

 the opposite valve, the anterior one direct, the other directed towards the posterior extremity of the 

 shell; lateral teeth slightly curved, moderately thick. 



Locality. Wabash river. 



A single specimen of this very distinct species, presented by Mrs. Lucy W. Say, 

 is in the collection of the Academy. It has dXmo<s,iXhQ o\\\\\neof Margaritana arcuata. 

 It probably belongs to sub-genus Cunicula. 



U. SUBCROCEUS. PI. 27, fig. 1. — Oblong, ventricose, rather thin; umbonal slopesomewhat inflated, rounded; 

 ligament and basal margins nearly parallel; disk slightly contracted from beak to base; posterior margin 

 obliquely truncated above, extremity rounded; basal margin slightly rounded; beaks witli small closely- 

 arranged obliquely concentric undulations; within whito ; cardinal tooth of the rightvalve direct, thick, 

 obliquely striated; anterior accessory cicatrix large, compressed, suboval, not confluent. 



Locality. One of the tributaries to Canadian river, Arkansas. 



This species is nearly allied to U. Sayii, but is a larger, thicker shell, with more 

 robust cardinal teeth, is proportionably longer, more ventricose, more obtuse poste- 

 riorly, has a darker colored epidermis, and the undulations of the beaks much smaller. 

 The epidermis is much wrinkled posteriorly. 



Dr. Woodhouse found several specimens of this species. 



U. NOBiLis. PI. 27, fig. 2, 3. — Ovate cuneate, ventricose, thick anteriorly, thinner pos'.eriorly ; valves 

 deeply furrowed obliquely, tubcrculatcd ; umbonal slope carinatcd above, biangulatcd inferiorl}', 

 tuberculatcd; posterior side subcunciform, rounded at the extremity; posterior end oblique, emarginato 

 in the middle ; basal margin profoundly emarginato; within white; cardinal teeth thick, prominent 

 and striated. 



Locality. Bayou Teche, Louisiana. 



This fine species has probably been regarded as a variety of U. quadrulus, but it 

 has a deeper furrow than that species, and becomes produced posteriorly, which never 

 occurs in the old shell of V. quadrulus. It is, also, more convex, and with tubercles 

 very different in form and arrangement from those of the latter species. The young 

 shell is subequilateral, not produced posteriorly, and the umbonal slope is prominently ■ 

 carinated. The old shell of U. apiculatus frequently presents a striking resemblance 

 in outline to a variet}^ of this species, but is always much less in size. 



U. PECTiTUS. PI. 27, fig. 4.— Oblong-ovate, thick anteriorly, thin posteriorly; posterior side cuneiform, with 

 a broad slightly-impressed furrow; basal margin contracted posteriorly; anterior side very short; 

 ligament margin very oblique; epidermis smooth, olive-yellow, with numerous bright green rays; 

 within very white; cardinal teeth thick, lateral teeth robust, (male.) The female is subquadrate, 

 ventricose; posterior cud direct, cmarginatc, inferiorly serrate; umbonal slope undefined above, tumid 

 infcriorly, longitudinally striated and serrated at base. 



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