FROM THE CRETACEOUS FORMATION OF NEBRASKA. 399 



although there are in the details of internal structure slight differences between the 

 ovate forms from the Upper Missouri and authentic specimens of B. ovatus from New 

 Jersey. 



Inasmuch as the figures and descriptions heretofore published do not fully charac- 

 terize the species, or enable the student to distinguish these from allied forms, we have 

 endeavored in a manner to supply this deficiency. 



BACULITES OVATUS. 

 PLATE V. FIG. 1, a-c. PLATE VI. FIGS. 1-7. 



B. ovatus, SAY, Jour. Acad. Nat. Sci. Phil., Vol. VI. PL V. figs. 5, 6. 

 " " Amer. Jour. Sci., Vol. XVHI. PI. I. figs. 6, 7, 8. 

 " " MOBTOK, Synopsis, 1834, p. 42, PI. I. figs. 6, 7, 8. 



Shell elongated, section ovate, sometimes a little flattened along the ventral side ; 

 dorsum marked only by lines of growth, which, passing around, continue obliquely 

 downward for about two thirds of the distance across the side, where they curve gently 

 upwards and pass over the ventrum in a broad arch, thus marking the outline of the 

 aperture. The ventral half of the shell is marked by somewhat regular, transverse 

 undulations, which follow a curve parallel to the lines of growth, dying out entirely 

 or passing into the lines of growth on the dorsal half of the shell, but are sometimes 

 more or less continued upon the ventrum. Aperture (as inferred from lines of growth) 

 having a linguiform extension in front on the dorsum, deeply sinuated at each side on 

 the ventral half, and broadly arched upwards on the ventrum. 



Septa symmetrical, lobes in pairs (excepting the ventral lobe), of moderate depth ; 

 dorsal lobe wider than high, very little shorter than the lateral superior lobe, divided 

 into two widely separated branches, each of which is tripartite, and the divisions sub- 

 digitate. Dorsal saddle as long as, and somewhat wider than, the superior lateral lobe ; 

 deeply divided at the top into two nearly equal parts by the accessory lobe, each part 

 is again subdivided into three or four branches with sinuate margins. Superior lateral 

 lobe as long as, but narrower than, the dorsal saddle, deeply divided at the extremity 

 into two parts, and again laterally divided, so that each side presents two principal 

 branches, the terminal ones of which are bifid at the extremities ; all with margins 

 sinuate and sub-digitate. Lateral saddle same in form as the dorsal saddle, and the 

 details of the ventral side of the one agree with those of the dorsal side of the other 

 respectively. Inferior lateral lobe wider than the superior lateral lobe ; similar in its 

 divisions, except that it is more deeply divided at its extremity in the centre, and the 



