MliK \\< Ml VTA 

 -I'tnlft | 



I pper Silurian form- now referred t. it l.ring luit impoverished remnants of the 

 powerful .-tuck tliat preceeded them. 



x liave l>een placed under Cyrtodonta or Cypi \\ i* 



n-ually conM-iere.l a> identical, that have no right there. Thus of forty-nine species 



'i.i I at CypriomKta K\ B. A. Miller in the 1889 dttkmol hkNortfi \mei- QeoL 



ami 1'al.. only eleven can with reasonable certainty be said to belong to Cyrtodonta. 

 These > /en*!*. Inironetuis, rugosa, spinifera and xubcarinata, all 



iKe.l l'\ Milling V/y//,i Meek and Worthen, and C. obtusa, $affordi, suban-in- 



ami snlisiHifulntn of Hall. The remainder belong to \Vhitflla. Ortonella, Vanux- 

 in and .\ftxlinlodon, or are too little known for positive generic placement.* 



EM mentioned we must add seven that have been described 



since the pnMieation of Mr. Miller's list: also fifteen new species, of which ten are 

 published in thi* work This makes a total of twenty-six valid Lower Silurian 







species positively known to have the characters of the genus as above defined. 

 Two I pper Siluriai , us Hall ami .17. jirtmigenia Conrad, ap., 



fall under Cyrtodonta. These have unusually thin shells but their binges are 

 essentially as <lemam!e.l for the genus. 



A few remarks are necessary to explain my adoption of Cyrtodonta instead of 



<'on nul's Ci//>rir>ir<liles as the name for this genus. Conrad's name hits seventeen 



' iority over that proposed hy Billings, but it was not until 1859 when Hall 



"lin-ed a sketch of the hinge that had been overlooked among the manuscript* 

 left l-y I'onrad that any adequate idea of his genus was possible. In the mean 

 time i ;>">>! Hillings proposed and fully illustrated his genus Cyrtodonta. In the 

 following year Hall published (in Pal. N. Y., vol. iii. p. 27, and 12th Rep. Reg. N. Y. 

 p. 10) his genus PaUearca in which he proposed to include precisely the 

 same group of shells. In the museum report mentioned (p. 13) Hall reproduces 

 Conrad's sketch of the hinge of irditts with the remark that both the descrip- 



tion ami figure of that genus as given by Conrad correspond in many respects with 

 /'"' -hdiil.l an examination of the typical species prove the two identical 



atvr name will give place to that of Cyfiri Finally in a supplemen- 



tary note to vol. iii ip. .Yjl) he again uses this cut ami now adopts CypricardUes in 

 place of hi-/ .1 ml Hilling*' two genera Cyrtodonfa and Vanuxemia. I have 



not noticed that the Canadian geologists have given up the use of Cyrtodonta. In 

 the United States however, with a few exceptions all use Cy]-ir,ir<H/>:* instead, 

 while of European authors Uigsby adopted Pa/awmi and the majority of the otl 

 < 't/r/o<!t>H(a. 



Tbr following belonc lo HTWtaBn: klitdivtd plrfwirtof BUlinti.; DMpOMtomii vat qtutmftlarl* of Whllflvld: Ur^ln^Hiti 

 Meek ud Worxbeo: ud WMHMM of BalL Tb nw g~*r OrU~tU l to*Ar4 mfam C. ***-! t. A. Mlllrr C.MB^MMM 

 Afford, ud Hlata. imMnmhH mad rrtuii*ilii Hall, bclonc to rowmmte. white C. va*n and lu*mt at tefford twfcwc to UM 



