668 



v . . . ..-... 



M ..... :t v ' n. >/.. 



17 nl It. 



The ti^'iirc- pre-cnt -n.-h ;t reiiKirkaMe valve that I am quite unal>lt> to account 



for it- peculiarities. I 'nfort unately the original of tin- ilra\vin->. which were nia-le 



f'" D niMai.l or lo-t.sothat I am ol,li K ,-,| to piil,li>h tin-in without 



a tinal verification of tin- character* -hou n. It may really In l.ut I louht. 



it. Or it may I..- related to I ',,. With more matt-rial it* allinitie- may I.ecome 



the hope that collectors will -earch for ami p.-rhap- -ucceed in 



;iat ha- in.luced me to retain it in my report. 



Muni (lt>,mi.lirty:i UH|) of th.- Tr.-nt..ii shal.-s, ,,.-:ir Kounialii 

 rienoU. 



'i- M \< LA, n. p-n. 



,i|.ai-- convex, semicircular or -.-miovate. with a lon^'. nt-.irly straight, hin^c; 

 valve* equal, full centro-.lur-ally, wit hout ri-l^es or asulcus. hut exhibiting a -moot h 

 -iil.central >|.ot when- the oniami-nt i- omitted; surface, in the only species known. 

 coarsely punctate. 



Type: l / . n. sp. 



I saw no way to escape the responsibility of erecting a new genus for the fol- 

 lowing -pecie* without forcing it into one of several that I am fully persuaded ought 

 not to receive it. The Ion-: hinge, semicircular outline, and almost perfectly equal 

 en. K ren.lerintf it .litiicult to .listin^ui-h one from the other, give it an expression 

 peculiarly its own. A'/>/% pfrmiunn .lone-, it i- true, ha- a -omewhat similar form, 

 Imt like all the ipeofel of that genus, it has al> a rnar-inal ri.lge and a subcentral 

 [it. neither of which are pre-ent in the species umler consideration. Still, the 

 -mooth -p,t m,.ntione.l al.ove pnil.ul.ly represent* the pit of AV,-/./,,/,/. ;m,| it i- with 

 thi- p-ini- that I think the atlinities of ,/r/A; lie rather than with either 



liit.s or Iwhilinn. The 1-,,,-lnlhxi ',, n 's ririch (.lour. I'ir Nat 



'1. 13. |.. IvJ; IV.HI) fn.in the l',-vonian at the falls of the Ohio, may be 

 congeneric with .17 : i. there being >ome similarity in their outline-, hut as 



the surface of the Hcvnnian form i- tly -mr,oth ami not inllate.l ,-entro- 



dorsjilly. I hesitate to say it is. 



