79 



mesial fold; the hinge-plate divided, and supporting two large conical spires which un- 

 directed into the hollow of the dorsal valve. 



Two species of tliis -enu.-. viz.. .!. fLinn (, and ,/',-/./ .-y///^.w (Hall), (if. 



indeed, the latter is truly distinct from the former) are known to me as occurring in the Cor- 

 niferous and Uamiltoti Formations of Western Ontario. 



94. ATRYPA KETICLI.ARIS (Linm< . 



nti<-ul'iri.< (Linna-us . Syst. A"/.. I'M. XII.. p. lliJi'. 



j4ti-ii/l /,(/ ii/'iri* (P/alman ', i"- . .1 . ;'/ '/., PI. IV.. ti_r. 1'. 

 T> i->l-r<(liil<i j>i > ' \ on Bueh '. > r i- ' i\itnl'i, p. 71. 



T. ,-. l.ntiulii (Atrypa) prisca i Phillips), /'.//. / '( '0rntm#,&o., PI. XXX11I., li- 1 u. 



(D'Urbi-ny , Prodr. /' '///., Vol. I., p. !'L. 



Atrypa reticularu > I>avid.-om, ]!ntt*h I-'uxa. Brachiopoda, lnti-<hidton, PI. VLL, f. . 7 

 ft. and Part VI . p. : 



^iiii-i'/i'i-iii'i (McCoy), /'///. /"/. Foss., p. 379. 



i reticulari* (Hall,, /'V. A. }'., Vol. III.. PI. XLII., fi-. 1, and Vol. IV.. Pin. 

 LI.-LIU, A. 



,H. 'arts (Billings), Canadian Jmniml, AM/- Si . Vol. VII., p. iMil. li. 



87. 



(The above list comprises only the most important of the numerous synonyms of thi.- 

 persi~ti-nt and oosmopolitan speci 



Shell exceedingly variable, both in form and dimensions ; usually oblong-ovate, with tin 

 widf-t portion of tin- >hcll a little In-low the triage-line. Ventral valve usually modij-at<-l\ 

 convex in the vieinitv of the beak, tiald -m-d towards the -idi--, and markedly def.rc-M'il in 

 front, with occasionally a hroad but shallow sinus towards the l'r..nt in;jruin. At other tim.-.- 

 the anterior dcj.ri -ion and sinus are ineon-pieiinus. The beak of the ventral valve -[null, 

 incurved, and so :ij. pressed to the dorsal b.-ak as to conec-al the minute foramen by whieh it is 

 perforat'-d. l>or--d v.ilve always convex and unifornily more so than the ventral valve, though 

 gometiiii'-- only sli-htlv so; usually very i. p iblioii>, hut breuminL: slightly concave t.iwn- I- tlu- 

 round--'] eirdin il an-l--s. and for the mo.-t part without a defined told correspondin,' with 

 Lhe siini- in the \vntr.d valve. 



Mirt'.ie,- envi-n-d with -mall radiatm-.' rounded ribs, generally two or three in the width of 

 a line, in'TeasiiiL' by hifuM-ati.in and interstitial addition in proceeding fr^m the be:ik^ to th> 

 front unrL'in. 'I'he radiating ril an- eni.-d by nnmerou.-. concentric line- of -rowtli. which 

 u-inllv form distinetly I'levated or jiroduced and s.pi ainose line-, and which, near the mar-in, 

 are MiHicinitly cloe to '_MVC the rib- a ehnraet'-ri-tie nodo-e appearance. 



In the interior of the ventral valve i- a broad mesial spo.ui--hape.l d.|.rc--ion, which 



dually -/rows shallower in proe.-rdnr_ r I'm in the l"-ak to ihe margin, and which is bounded 



by two well d'-lin.-d -micirciilar rid^-s. 'I'hi- givBI origin chietly to the divaricat r : 



and givei rise ' R OOrrespOnding elevation, bounded by two Bemioirouluf depre->inn-< in the 



' of the valve. The int'-rior of tin- dr-al valve i> chietly oeeiij'i.-.l by the -_'rcatl\ d. \, 1,.| , d 



l -ujiport- of the arm-. 



1 . from the middl" of the Silurian -eri.-s to tin- summit of the 



ni .11. and i-a well known -hell both in Kurope and Norlh America. In \Ve-t.-rn (Mr 

 it .,. -:irs plentifully both in tin- ( 'ornifei-" i- l.im .nd th.- Ilimibon (Jroiip. \ 



rule, the ( 'orn ili roii', x nnj.le- are ofl,r and have more 'jibb.i.i, d^r- il TalVOfl th in 



tho-e frnin the 1 1 unili'in -erie>. An avr i ' Hamilton speeimeii h t width ol ten 



line-, it- l.-n/'h bein_' tin- .- mi'-, and il- h'-i -|,t bein- live |i !: \ M aserr.-e -|.eeim.'ii from 



the ( 'urn if- -roii- In- a greatest width of thirteen lines. A 1 irj-er specimen from the - me 

 uiiti'Mi, \\iih a m.ire -ili'h.ius dor- il val\e. h ' mrtci-n line-, a length 



line-, and a h'-i -hi nl thirti en Hi 



' rniferoiis I/nne-t ,i ..... f |',, r t ( ',,!bonie. Kid |] 



ville \e. l|.-imil'..n liroiip ol' \\ i Id'-r. and K.i.-th 1 ' Is, near LrkODI m the Town 



if I! . aii'jU' t. 



