regularly but not greatly convex, depre-sed towards the cardinal angles. Area narrow, linear, 

 without foramen ; beak small. Dorsal valve concave. 



Surface shining, smooth, without radiating stria?, but with very faint concentric lines 

 of growth. 



" The muscular impressions in the ventral valve extend more than half tin- length of the 

 shell. The divaricator muscular imprints are deeply depr. sa d, eli.n-ate ovate, narrowing 

 above, and somewhat widely separated below; while the ocdusor iin] iv-.-ions are narrow 

 ovate spots on the thickened portion of the shell, and below these extends a narrow elevated 

 band separating the other impressions. In the dorsal valve, tin- anterior and posterior oeclu- 

 eor impressions are small and not strongly defined. The cardinal proce-.- i- .-lender, bifurcat- 

 ing. with a narrow rounded ridge extending from its base down the middle of the valve. The 

 interior of the shell, excepting the muscular impressions, is studded with ] ruminent scattered 

 oranules or papillae. The emulations on the hinge-line are rather di.-tant but conspicuous." 

 /"Hall, Pal. N. Y., Vol IV., p. 104). 



Mcrea is readily recognised by its general form and sim "*h 

 surface, and, when the shell is preserved, by its pearly lustre. It is nearly 

 allied to the ,S//vy /<//"/' (Oiihin) /</</. of Bronn, from the ]>evnnian Hocks uf 

 Europe; but according to Hall, it is distinguished by being much less ili -- 

 Stnphamena tinctly striated, and by having only about half as many crenulations on the 

 " f hin"e line. 



uituriil M/e. 

 ifiTousLinif- 



toae. 



Locality and formation. Rare in the Corniferous Limestone of Port Colborne. 



82. STKi>rHMi;\.\ IMlo.MBOIDALIS (AYahlenbcri: .). 



This well-known species is so familiar to all students of Pal;, o/oic (ieoloj-y. and its char- 

 acters are so readily recognised, that it seems unnecessary to occupy space here with a des- 

 cription of its peculiarities, or a recapitulation of its ponderous synonymy. It may. a* a 

 rule, be determined at once by its rhomboidal form, the deep eoneentrie wrinkling of the vis- 

 ceral di.-e. and the abiupt <:cniculatio!i of both valves toward- the dor-al side at a point -itu- 

 atcd at from one half to two thirds of the length mea-un-d from the beak. >'. /7 * i* 



known to have commenced its exigence u early as the l.o\v.-r Silurian period : it i- n 

 abundant Upper Silurian fo.-sil ; it is found throughout the Devonian : and it even extu 1- 

 into the Carboniferous rocks. 



I.i,'-nlil>i inn! !'nr:ini(i"ii. Common throughout the Cornif'erons J ime-toiu 1 of We-t.-rn 

 Ontario. Al.-n in the Hamilton group of the same district, though not known in the Hamil- 

 ton series of the State of New York. 



Q & STKM'TnKiiYV nrs (King). 



The -_'enu^ Str> i>t<>rlDiii<-lii< includes BtrophomeDOid .-hells of a M mi eir.-nlar or M-mi- 

 ellipti'-'d shape, " OODOaVO-OODVeX OT pUnO-OODVei, and BOmetimea with both valves convex ; 

 th'-v are externally -triated witli roinnli <1 liifnreating thread-like -tri:r. which are ere. ,1 

 by fine c. , tie. -nine line-; and in -oine t'.n-in- the stf>n -.T -tri:i- are ili-tant. with liner 

 railiatiii'_' and corei-ntric stri:e eanec Ihititr/ the intermediate BpaOBB, Tin- \entralbeak i- 

 BOinetiiiH-- y.roduc.-il and bent or twi-ted, and the (i--ni-.- b-tn-atli the beak i- <-lied <-r ; -ir 

 tialh i-li-.-d by a -"li'l <\> Itidiiim, while the area i-- -uhjeei t.. vi'-:it variation. A narrow 



Often eZIStC on the dnr-al valve, but tliis i- not a constant .-liaracter." illall. /'<;/. 



.V. J'.. vol. iv, p. f,i 



Tlie '/'-nil- S>j,i,'i,rJi i/nr/i/i.-: is very rlo-ely allied to StrophomtHQ proper, the mo-t obvi 



rnal charai'ter by which the fomi'T is distinguished being the irregular twisting of the 



lieak of the vi ntral valve. 'I'he /.nn- i- P-pre-mted iii all the '.-i.--it pall I'ormation-. 



from the Lower Silurian upward-, and ap; be \,-ry alnindaiitly r.-i r. - nt.-d in the 



J> .,ini:n] l;.,e|.- ,,( North Amerie-i. K) fu a- ii di\ iduaK are cnii.-,-i n- d. l'i..t'. Hall, h * 

 cv.r. refers all the I)evonian I'.rm- nt'thi- nOUB '" '-nr . \ . -.-din ly nu | 'he 



,V//-./''"/7i(/m7i//.>' ('It. inn of < '..nrad. Onlf OttO form of the gTOUp b : ded a< 



yet 1'iom the I>. \oni-m lloek-of Canada, namely, the >'. /' of M i I'. 



