i i:i'H.\i .<>!-, 



pretty much the entire body -chamber. Its dimensions are 21 by 9 ram. 

 The distal extremity which exposes a septum i> 1" l>y "> mm. 



Tlii- -pecies is readily <li>tinguished by its distinct arcuation, rapidly expanding 

 shell ami the great difference in the convexity of the sides. 



Formation and loalitg.lo the Trenton limestone, Cannon Kail- Mmm-sota. W. II. Srotli-ld. 



TRIPTOCBRAS ;< 



There is a single specimen, an internal cast of the deep body-chamber, bearing 

 :i M-ptinn at is distal extremity, which presents differences from any of the foregoing 

 species. The convexity of the septa and sides is about the same as that of T. 

 l>/'inoconvexum but the inclination of the lateral margins is greater, with the sides 

 acutely angled and almost carinate. The body-chamber, also, is distinctly arcuate. 

 It nearest relations are with this species, as it is decidedly less convex and less 

 r.ipi-lly tapering than T. oweni. The single specimen is from the Qalena horizon 

 near Cannon Falls, Minnesota. 



Hillings described two species of this genus from the Trenton series, vi/.: 

 Ortlimra.* :ifihi<is*, and 0. hastatum^. In the absence of illustration it is difficult, 

 ft m the not very precise descriptions, to establish their specific traits. The former, 

 /'. iphins, appears to have the lateral angles obtuse, in which respect it is unlike 

 T. planoconvexum; its convexity is less, its size and apical angle much greater than 

 in T. oweni, while its lateral margins are less blunt and its venter less flat than 

 in T. planodorsatum. In T. hastatum the lateral angles must be even more obtuse 

 than in T. planodorsatum, the shell also tapering more rapidly and the septa being 

 more convex. 



The Orthoceras servile BillingsJ, from the Quebec "group, is a Triptoceras with 

 rapidly tapering margins and rather convex sides. 



TRIPTOCKRAS LAMBI Whiteaves, 1891. 



I'l.ATF I.VI. FIOB. landl. 



Gonioffrat Iambi WIIITKA VKS, 1891. The Orthoceratlde of the Trenton limestone of the Winnipeg 

 Ita- -. Royal Soc. Canada, vol. Iz, sect, iv, p. 86. pi. xi, flgs. la /. 



Shell large, biconvex and lenticular in transverse section. Convexity of t he- 

 sides subequal. that of the dorsal side being slightly the greater. Ventral -!! 

 slightly flattened medially. Dorsal and ventral lobes broad and regularly convex, 

 deeper on the dorsum, the general convexity being more decided than in the otln-r 

 species here noticed. Saddles acute, more distinctly so as viewed from the ventral 



KvpuUeol. Burr. Cad. for lh j*r UH, . IM. UBT. 



