NATURAL SCIENCES OF PHILADELPHIA. 177 



Ammonites placenta, var. intercalaris. It is possible this shell may be spe- 

 cifically distinct from A. placenta of Dekay, but it agrees with that species so 

 nearly that we are in doubt about the propriety of considering it entitled to 

 rank as a species. It differs externally from the typical forms of Dekay's 

 species, in being rather less compressed, and in having a slightly larger umbili- 

 cus, while instead of a single series of scarcely perceptible transversely elon- 

 gated prominences on each side, it has a row of small, but distinct nodes a 

 little less than one-third of the way across from the dorsum, and another more 

 prominent series near the umbilicus. It also differs in having a row of small, 

 pinched, alternating nodes on each of the two dorsal angles. 



With these external differences, however, the septa of the shell under con- 

 sideration, are so very similar in all their details to those of A. placenta, that 

 we are at present inclined to regard it as a variety of that species. 



It is also worthy of note, that the form before us is closely related to A. syr~ 

 talis of Morton, being in fact almost exactly intermediate between that shell and 

 A. placenta, as well in form and external ornaments, as in the characters of its 

 septa. Its exact relations to these species can perhaps only be settled by a 

 careful comparison of a more extensive series of specimens than has yet been 

 obtained ; in the mean time it may be made known as a subspecies, under the 

 name A. placenta, var. intercalaris, and should it prove distinct, it may take the 

 latter as a specific name. It seems to attain a large size. Our specimen, which 

 consists of inner septate whorls, is 5-70 inches in its greatest diameter, with 

 a thickness or convexity of 1-62 inches. 



Locality and position. Sheyenne River, in the upper part of Formation No. 4 

 of the Nebraska Cretaceous series. 



Ammonites Vermilionensis, M. & H. Shell compressed discoidal ; umbilicus 

 large, very shallow, and showing about four-fifths of each inner whorl ; volu- 

 tions five or more, rather sharply carinated around the middle of the dorsum, 

 and ornamented on each side by nearly straight, simple, moderately strong, 

 obtuse costae, which show a tendency to develope nodes at each extremity. 

 Greatest diameter 1-05 inches ; convexity about 0-29 inch. 



Locality and position. Mouth Vermilion River, in Formation No. 2, of the 

 Nebraska section. 



Scaphites Warreni, M. & H. Shell small, transversely subovate, moderately 

 compressed, rounded on the dorsum ; umbilicus rather small; volutions sub- 

 cylindrical, height and breadth nearly equal, increasing gradually in size ; non- 

 septate portion of last turn slightly compressed laterally, and deflected from 

 the regular curve of the others, so as to become nearly or quite disconnected 

 at the aperture. Surface of the inner whorls ornamented by numerous small 

 costae, which increase chiefly by implantation, and all cross the dorsum very 

 regularly without arching; on the sides of the non-septate outer chamber, 

 about every fourth or fifth one of the costae is much more prominent and 

 sharper than the others, and extends quite across to the umbilical side, while 

 those between die out, or coalesce with the others at various distances. 



Length 1-45 inches ; height about 1-22 inches ; breadth 057 inch. 



Locality and position. Near the Black Hills, in formation No. 2 of the Ne- 

 braska Section. 



Scaphites nodosus, var. plends. We suspect the noble specimen we here 

 propose to notice provisionally, as a variety of Dr. Owen's Scaphites nodosus, may 

 prove to belong to a distinct species, but as we are not yet fully satisfied on 

 this point, it is perhaps better to regard it, for the present, as a marked variety 

 of Dr. Owen's species; and should further comparison demonstrate that it is 

 entitled to rank as a species, it can take as a specific name that by which we 

 have designated it as a variety. It differs externally from Dr. Owen's figure of 

 S. nodosus, in being greatly more ventricose, and snorter in proportion to its 

 height, while its inner rows of nodes are much smaller and nearer the umbili- 



I860.] 11 



