IDA s ll 



\nitcrtlieyare rurvd fur\v;ir<l into a l>ro;nlly an^'lc.i -.i'Mlr. wlndi i> not anitr. 

 t.ut i- -harper mi tin- -opta nearest the aj>erture. The depth <>f the air-chaml-fi- 

 on tin- M.I.- i- about one-half greater than on the doHura. The form of the suture 

 is so rharai-teri.-tir that, taken in conjunction with the form of the shell, I have 

 ventured to regard the specimen as representing a new specific form. 



IHmensions. Length, 30 nun.; major axis of apertural end, Hi mm.; minor axis 

 1 _'-.") nun : major axis of distal en<l I'.' mm.: minor axis, 10 mm. Average depth of 

 air-chamber on venter, 2 mm.; on dorsum. 1 ',111111. 



Formation and locality. la the lower Mm- l*il- nf tin- Tri-ninn .nn. -I..IL .it Janeivllle, WlHiii-m. 

 Regittrr, No. tt. 



.... Q1 i;m -Ki;.\S. ht'Koniii.-k. 1M1. 



liM<OCERA8 III l-I.H-H-o-TATI M H'/////rW'/, 



Gyrvcerat dupHcieoMtatui,! \\inniKi.l), 1878. Ann. It.-pU Oeol. SurT. Wi-< n*\n fur 1877, p. 78. 

 Ogroeerat dupHeieottalvm WHITFIKLU, 1882. Geology of WlHconsfn, vol. . |<1. MI, 11^. 1. 



Fragments of this species occur in specimens in the state museum, rolleci..] 

 from the lower blue beds of the Trenton limestone at Janesville, Wisconsin. The 

 original -pecimens were from the Trenton at Bristol and Heloit, in that state- 



Family TjENOCKKATI I >.!:. 

 Genii- KIIIVSruMli liroeder. IsiM. 



Kl KYSTOVlTh- I'MIATUS EIHHKIII*. l^l'J. vai. OCCIDENTALIS Hull. 18fil. 

 tt* umlatut. var. occidrnt'ili* HAI.I.. 1861. Kept. Supt. <;.! Surv. Wix-nnsio, p. 38. 



This well known f>rm i- represented by several specimens in the collections 

 before me, some of them of large size, all possessing the broad whorls with flattened 

 dorsum and the simple concave septa characterizing the western variety of this 

 species. The New York specimens upon which the species was founded, seem to 

 be restricted in range to narrow limits within the Black River limestone formation 

 but the specimens from Minnesota indicate a more general distribution. Two 

 large examples have a diameter of about 140 mm.; smaller specimens show the 

 extreme ventral l>nt suhmarpnal position of the sipho and the dorsal depression or 

 groove on each whorl made by contact with that next within. 



The species has usually been referred to the genus LHuHf*. Hreyn. the t yjte of 

 which is Litnitr* litnu*. It is evident however that the species is not a Lituites, and 

 and I have here followed the recent suggestion of Hyatt* that it be placed with 



t'r mition and locality. In the Tn-nl<>n limestone at Minneapolis, Spring Valley, Northfleld. 

 Island, Minnesota: Dlxon and Roclcton, Illin 



Xu*eum Regitter, No*. 6066.'.: M 



Proo. Amr. Phlo. 8oc.. rol jzitl. p. Ui. UM. 



