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PEOTEIT (GHLAJnS) AlvIEIiiUS n. sp. 



"Jescript iOii .- Shell small, siilDequivalve , suborliioular, the 

 height and v/idth virtually equal, well inflate'!, the two valves 

 equally inflated; the dorsal half, etoluding the a^.rieles, forming 

 a sector of rhout 95'-*, the ventral half evenlj? suhcircular ; "both 

 valvf^s sculptured with twenty-one to twenty-three strong, suhround- 

 ed radial rihs, separate^ by narrower interspaces; concentric sculp- 

 ture of fine raised lines usually appearing in the interspaces and 

 occasionall;: on the rihs ; suhmrir^ins without radial, sculptu.re; auri- 

 cles uviecu-~l, hoth hearing inconspiciioua radials, on the posterior 

 auricle more prominent vei-trally, hut on the anterior broader and 

 stronger dorsally, overriden by fine conc;entriclines, coarser and 

 more irregular on the anterior auricle. 



Dif.'.ensions .- '. right valve: ":t., 15 mm.; alt., 14.8 mr.i. ; 

 diam. , ?.? ram.; length of >ii!=3-e, ^ r-m. A left valve: lat., 

 1^'.5 ram.; alt., IS. 2 mm.; ^iara. , 5.5 ram.; length of hinge, G.2 ram. 



Hemar>s .- P. an: el e us is well represented, althouf^h indivi- 

 diials are not as numerous as those of the other member of this 

 section. '2he characters are constant except for a slight vari- 

 ation in outline which causes some specimens to be slightly less 

 rounded then the typical form. G'^'-^'-^^ionally a slight sulcus ap- 

 pears on the extreme distal portion of the ribs, but this is a min- 



