Nc.iivj ciMiu.'j.ix liiriciiioroDA nwicorr. 4I3 



iidditioii 1,0 tlic coiicciitric liiicN of growth; tlic. iiiU'rior of \\w nIicII as 

 hIiowii l)y the caMtH waH Hlroiij^Iy piltr*! or puiicliilc, flic puiujtic beiiij; 

 aiTanj;;c(l in coiicontric. linoH followinjf tlu' liiiCH of H^rowth. TIm', shell 

 is reliitiviMy thill and formed of ii thin outer layer and oiur or more 

 Miiii iiiiiei- laytU'K or iaiiK'Hii-. 



The typo si)0(!iineii ol' tiu^' venti'al valve has \v lent^tli of !> mm,; 

 width, <»..') mm. An associalcd ilorsal valv<^ has ii lenjitli of 7 mm.; 

 uidtii, .").."» mm. 



The only interior that shows anythiiiH" more than the piinetate siir- 

 faee is that, of a dorsal valve. In this the area is partially shown; it 

 is relalivt^ly short and marked liy fine stria- parallel to its hiise, and 

 I W(> imjK'i'feetJy d<'V(^lope(l llexnre, liims. TIm^ cast of a, narrow median 

 septum is well shown and on each side of it the middle liiteral miisele 

 seal's. The path of advance of the<;entral muscle sears is (|uite plain; 

 also one of the scars. Tlu^ only tractes of tlui vascular Hyst/cm is a 

 portion of a main vascular sinuH. 



(HtKcrvalUmH. — This is a very pretty and distinct Hpeeies that occurs 

 in I he iiit('rh(^<ld<'d linmstones of the Se<'rel (/anyon shale. 



l<\>rin(iliouM (iiul localllji. — Middle (!aml>iiaii, upper beds of the Seci(;t 

 Canvoii shale, east side of New York and Hecret <'.anvoiis; at the TOO- 

 fool, level of the Kichmoml Mine, l.'iiiiy Hill, I'jireka District, Nevada. 



A somewhat similar, if not. identical, vi'iitral \alve oi-ciirs in tlui 

 npp(n' beds ol the Prospect Mountain limestones on the east slope of 

 l'i'ospe<t Mountain, Ntnv Yoik Cannon. 



Tupc— No. L'T.J.jr), 1 1 .H. N . M . 



OBOLUS (LINGULKLLA) KOGERSI. new spccicH. 



(Jeneial form <dont;ale-ovate, with the veniral valve suhacuminate 

 and the dorsal valve ovate in outline. There is coiisid(^rahI(!i raii^^c, of 

 variation in tin; outline of the valves, owiii^^ larj,Mdy to distortion 

 api)arently produced by iiiov<uneiit of the matrix. The convexity of 

 tli(5 valves is fairly stronj;- and nearly tlui same in both, except that the 

 dorsal valv(^ lairves more abruptly inward toward the beak. 



TIm! outer surface ol the slKill usually adheres to the matrix, but in 

 three specimens i)oitioiis o( it are pres(Tved which show that it is of 

 essentially the same character as that of (>. (//.) Hloiiitinns. The siir 

 face is foiiiie<l by very line concentric lines and stria- of growth cntsscd 

 transversely by stroiij>' iiiidnlatinj,', slijfhtly lamellose lines. VVIien the 

 (»ut(M' layer is exfoliated the inner layers are marked by concentric 

 lines of ;^rowth and line radialiiij; stria'. This is also ihe cliaractcir 

 of Ihe inner surface, so far as can be determined from the specimens 

 ill the <*,ollection. The shell is rather thick and biiill up of a thin oiitcrr 

 layer aini several inner hiyers or hiiiKflla-, the latter becomiiif;' incnias- 

 iii;ily numerous toward the front. The laij;est dorsal valv(^ in the 

 collection has a leiif^th of l.'J mm., with a width of 11 mm., and a smaJhu- 

 vential valve with a lenj^th of VI mm. has a width of 1) mm. The 



