TO JUNCTION OF GRAND AND GREEN RIVERS. 141 



Large size and character of surf ace, this shell approaches P. Missouriensis, Swallow, but 



is apparently something smaller and more elongated in outline. In P. Missouriensis 

 the width of the base is greater than the height, while in our species the reverse is true. 

 In the Missouri specimen, which I saw in the hands of Governor Gilpin before it was 

 described, the whorls are so iitted together as to produce smooth and somewhat con- 

 cave sides; while in P. cxcclsa they are shouldered, and the outline of the sides is 

 straight or slightly convex. 



Formation and locality. — Upper part of the Carboniferous formation, in the canon 

 of Grand River, near its junction with Green River, Southern Utah. 



Lamna Tex an a, Roem. 



I.amita lixauo. Koeiiicr. Kre'ule v. Texas, p. 21, taf. 1, fig. 7. 



Found in company with Ptychodus Whipplei on the banks of the Canadian, at 

 Galisteo, and at the Paffosa in the "fish-bed" near the base of the Middle Cretaceous 



series. 



Oxyrhina Mantelli, Agass. 



o.ryihiiHt Mantelli, Ag., Roomer, Kreide v. Texas, p. 29, taf. 1, fi^. i*>. 



This species occurs iti the fish-bed of the Middle Cretaceous (No. 2 of Meek and 

 Hayden's section) at the Pagosa. It is somewhat doubtful, however, whether it is 

 really identical with that described by Agassiz. Probably more material will show^, 

 that it is distinct. ,4 ^v 



( )TOZAMITES MaCOMBII, Newb. 

 Plate IV, fij,'s. l, 2 ; Plate VI, tigs. 6, 5\ 



Frond pinnate, pinnae opposite or subalternate, approximate or imbricated, entire, 

 sessile; lower ones small, reniform, or circular; upper large, oblong, rounded, or trun- 

 cated at the extremity; base nearly as broad as apex, very slightly auricled and 

 rounded at upper and lower angles, attached to rachis by two-thirds to three-fourths 

 of entire breadth: nerves numerous, iine, but distinct, equal, forked, radiating from 

 the attached portion of the base to all parts of the lateral and apical margins ; rachis 

 slender, smooth, or finely striated longitudinally. 



The outline of the entire frond is linear-lanceolate; different ones varying much in 

 breadth and in the spacing of the pinnules. At first sight, they seem to resemble closely 

 those of several of the Cycads of the Oolite, Wealden, and Chalk, but on more careful 

 examination they will be found to present characters widely different. The oblong or 

 quadrate truncated pinnules, increasing in length from the base upward, at once sug- 

 gest the species of NUssonia and Pterophyttum, to which I have alluded, such as V. majus, 

 l\ minus, P. Sckaumbergense, NUssonia compta, &c, but the nervation (tine, equal, fork- 

 ing nerves, radiating from the attached portion of the base to all parts of the lateral 

 and terminal margins,) and the mode of attachment to the rachis — each pinnule being 

 distinctly separated from the others, the base slightly auricled, with rounded lobes — 

 exclude it from both the preceding genera as at present constituted, and associate it 

 with that group of Zamites (Brong.) which form Fr. Braun's genus Otozamitcs (Oto- 

 ptcris, L. & II.). From all known species of that genus, it is, however, somewhat 



