Go 



oearly flat. Area of the ventral valve alwut one line wide at the beak, that of the dorsal 

 valve being about half as wide. Both areas are striated, and they form with one another an 

 angle of '." >~ <>r a little more. There is no foramen, but sometimes a flat triangular space with 

 a narrow median callosity. 



Surface with numerous fine, equal or sub equal striae, which increase in number in pro- 

 ceeding from the beaks to the margins, both by bifurcation and intercalation. Six to nine 

 stria- occupy the space of a line ; and these are crossed by close-set concentric stri;e, from 

 ten to twelve in the space of a line. Be-id--< the close cancellation thus produced, there 

 are often irregular concentric undulations of both valves, and sometimes the bases of minute 

 spines can be detected. 



Avera-je , xamples have a width of about an inch by a length of about three quarter.- of 

 an inch ; hut the width on the hinge-line varies fr.iiu half an inch to two inch' 



As regards the internal character-.. Prof. Hall states (Pal. N. Y. Vol iv. p. Iniii that 

 th' 1 int. -rior of the ventral valve is marked bv large flabelliform divaricator mu.-cular im- 

 pressions, extending more than half the length of the shell ; narrow above, \vith sid--s nearly 

 straight, curving below and deeply divide.! in front. . a<-li di\i-ion showing four or five lob--- 

 Tin -or impressions are two semi-oval elevated -pots a little below the apex, the centre 



beOOmiog a thickened ridiie or process lying beneath the place of the foramen, with a cavity 

 on each side for the insertion of the bifurcate dor- il cardinal pro.- --. * * The mus- 



cular impressions of the doisal valve are distinctly but not strongly marked ; these :av -. pa- 

 rated above by a median rid^e which divides in the bifurcating cardinal process, and this U 

 supported on each side by an oblique pustulose ridge which gradually merges into the sur- 

 face of the .-hell." 



Strophomena perplana (Conrad), belong to a 

 group of Strophomenoid shells separated ii\- Prof. 

 Hall from >//< >//////< r mi proper, to form a new 



mi-, which lie terms Strophodonta. Tlie c: 

 peculiarity of the forms include. 1 by Hall in 

 Ins genus Strophodonta is the absence of a foramen 

 in the area of the ventral valve ; hut a- the 



^/ f orms i,, ( | U ,..rj,,n ;i r.- in most respeote othcr- 



wi-e (indistinguishable from the typical ,-peciws of 



and), a A mcdiiiiii-iz.-.l ^'/M/////,////. //./, i i \\ \\\ ;id\ isahle not to regard 



mdi\ :.lu:ii, "i tli-: iuitnr.il ,}/. : n A i>rti>iii <>f tin- Mir- i i- \ . i 



,..,. i.,,,,,.,. Hu- peculiarity as being Ol more than at any late 



sub _.-n. ri v a, ue. S. perp - i remely characteristic species of the Devonian llo.-k 

 North America, and i- in Lf-neral r.-:dil\- ree i-nis. (! hy its flattened form, its tine equal ,-tri.i-, 



and the .-I oonoentrio striation of the surface in \v.-ll pr. - jpecimena. 



Ln,,iiiin mi, I Formation, Common in the Corniferous Limestone of Port Colborne. and 

 lot ;. Con. 1, Wainflcct. 



77. STIli.l'Mo.MK.NA IM M: - - < ' 'ad). 



Xtr-i'l. (Conrad. 1 , ././////. Af>l. -\ nt. N- . !'liUn'l,ti>h>a, \'ol. \'lll, p. 



358, pL II ti_'. II. 



ji/iui/i, ii 'i il, IH'IX -i (I I all i, 'I'.-ntli 1 1. -port (iii the State Cabinet, p. l.'!7. 



I (Hall), Keport on the (leulo-ival Sur\.-\ of Io\\a, j 1 '1 111. 



ti :. 



Slri>li IliliiiiL' ' . / ''hi!,. N.-w Serie-, \"..l \'l j, ;; 1 1 ; 



116 M-' 



. y ,/j//,,,//. demista (Hall). Pal A'. )'., Vol, IV. pi- 81, 101, 11 1. 



Sln-11 vr\ varial.l-- both in form and in diiiH'ii-ion-. The forin i- n-ually scini elliptical, 

 bat m ili quadr it.- or -lib tri iii'j-ular. I'-u.illv tin- widlli of the -hell c\.-. . d- the 



I'-nitb, but BOm iioth dim. n-'h.n- nn- .'qiial, and occasionally the width i- 1.--- than the 



l.-ii'tb. Th'- biir.'i- line i- ll-U illv .-qu il to tli.-in li width ot the -hell, 



and th'- eardinal an re often r\t.-nd'-d "r aiiri.-iii.it--. Specimen.- \.,r\ from a third of 



nn in.-h to ;m UK-)) and a half in width. 



Th-- ventral valve i, eonv-x -om.-tim.-. itfOt and th inv.-\it\ i- u-ua.!\ uniform 



nnd r. oii:,r f|-.,m (h,- mnho to the v--ntr.il margin. Th- . nc.i\e. 



5 



