i PHALOFODA. 



! 



the former are more abrupt than in any other species of the Ken us here not 

 None of the specimens are very well preserved, but the best of them retains nearly 

 all of the body-chamber and seven air-chambers. The dot-sum is very broad and but 

 -li^'litly arched. The seven aJr-chaml)ers occupy a length of 19 mm. on the venter 

 ami 10 mm. on the dorsura. The body-chamber is 23 mm. in length, 23.5 mm. in 

 major diameter at the base, and 2'J mm. in minor diameter. The great difference 

 in the outer ami inner curves gives the shell a decided ventricose aspect about the 

 base of the body-chamber. 



Tin- -piM-imens here described are in very close agreement with those upon 

 which \Vhittield based his species Oncoceras brevicameratmn* from the Trenton beds 

 at Beloit, Wisconsin. This is especially noticeable in the subcircular form of the 

 septum. This species is, however, much less ventricose on the body-chamber than 

 those which we here regard as representing 0. pandion. 



Formation and locality.- In the Trenton limestone at Janesville, Wisconsin, and In the vicinity of 

 Cannon Falls, Minnesota. 



Uttteum Remitter, No. 8303. 



Family CYRTOCERATID^. 

 Genus CYRTOCERAS, Goldfuss, 1832. 



Though fully alive to the fact that the multitude of middle and late Silurian 

 and early Devonian species which have been referred to Cyrtoceras, must eventually 

 prove to be an association of phyletic inequalities, we still feel constrained to 

 employ the term for a considerable number of the species here under consideration. 

 These forms have been studied with care by Hyatt and most, if not all of the 

 species here discussed will probably take their places within the genera intro- 

 duced by him, namely ; Ma-lonocercu, Oonoceras, Cranoceras and Eremoceratf , but it is 

 difficult in many cases to employ these terms with precision. In this author's 

 work Cyrtoceras does not appear as one of the "Genera of Fossil Cephalo- 

 poda.' l >ut the type of this old genus, C. depression, in assumed as the type 

 if t'ranocerus. Thi*~type-species is a middle Devonian shell, occurring in those 

 later faunas of the Paleozoic where such forms ususully lack any evidence of a 

 swollen body-chamlier. but are likely to possess extended and more completely 

 coiled tubes than in the Silurian faunas. It is among these later forms that the 

 di-tinction between the genera Cyrtoceras and Gyrocerus becm y obscure.t 



while in'the Silurian shells the presence of an inflated tube is common and the 



O*oUxr of Wlc.mlii. ol. Iv. P.M. pi. Tit. >f . t. 

 I'roc. Burton 8oc. Nt. HUt-. vol. xxll. pp. m-m. 



tStf Uif ramarki by Jamr* Hall upon lie luipowlblllt ( Itrtr nun.t-r of IVronlin >pr<-lM III. mrounrj 



nu: l'la< ni. lif> l.r.ptll- 



