"DA. s "'' 



I'jrrtocer*.* murum I 



the slight deopc-nin;,' of tlic air-chamherson the ventral -m-farr and also the recurved 

 surface striic which have a direction nearly the reverse of that of the septa. 



Formation and /vi/ify. In thr T:i-nt..i. Minneapolis and noar Fnun- 



uin, Minnesota, and Ii.-lc.it, Wisconsin; In the Galena shales at WykofT, Minnesota. 



Muofum Regittrr, Nus. 6S64, 7026. 



K.RAH CAMCKfJI //'I//, 1S47. 



ri.\ it i '.. . 



Cgrtoeerat eamumm II M.I.. IM; I rk, v..|. i, p. \\*\. pi. xi.n. fl. 6. 



Cyrtocmu camurum WIIIIMKLD, 188*. Geology of Wisconsin, vol. Iv, p. 231, pi. vn, UK*. 7, 8, 9. 



The very gradual expansion, slight arcuation and extreme lateral compression 

 of th: .-s afford a ready distinction from associated forms. The original 



-pecimen. from Middleville, N. Y., is not very favorably preserved, but that figured 

 by Whit Held serves to establish the characters of the species and with the latter 1 

 titul a close agreement in the case of a single specimen in the collections in hand. 

 This retains the entire body-chamber and sixteen air-chambers, and also shows the 

 bead-like divisions of the submarginal sipho. 



Formation and locality. la the upper buff beds ..f tin- Tr-nton liinentoni-, Samp's quarry, Belolt, 

 Wisconsin, 



CYRTOCKRAS HAI.UANTX D'Orbigny, 1850. 

 PLATE i.x. no*. 11. 12. 



"fcra* tinittllo*um HALL, 1847. I'.i! .1 .mt<,loj:y of N. Y., vol. I, p. 93, pi. XLI, BgH. 2o-. 

 Cfrtncertu kaUianuiu IKII: o. l' r Kl. de paltktntul. slratlRraph., vol. i, p. I. 



Cfrtoetra* billing* SALTKK, 1859. PiRurea and Descr. Canad.Org. Rem. Decade 1, p. 33, pi. vn, 

 flK. 5 (non 8). 



The original of this species was a small, badly crushed specimen distinguished 

 by its surface ornamentation, consisting of "undulating squamose lamellae 

 which are abruptly bent backward on the dorsal line." There are two specimens 

 before me in which this peculiar ornament is retained; one a mere fragment of the 

 shell with these surface markings very sharply defined, the other a considerable 

 portion of a large and more complete example in which the surface is less clearly 

 preserved. The latter shows an arcuate and broad shell with ovate cross-section, 

 the dorso-ventral diameter diminishing, in a length along the ventral periphery of 

 60 mm. (and dorsal of 37 mm.), from 25 mm. to 16 mm. 



Septa rather closely crowded, eight or ten on the dorsal surface of 37 mm., 

 inclining somewhat to the venter. Sutures with low, scarcely perceptible lateral 

 lobes. Sipbo ventral, submarginal. 



