370 



from isTebraska, as well as tliose found ia Xew Jersey, do not show any 

 essential variations in this respect. 



In the relative size, n amber, and arrangement, as well as in the mode 

 of branching, of its lobes and sinuses, the shell under consideration 

 agrees very nearly with authentic specimens of A. complexus ; though in 

 the details of the divisions of its septa there are differences from those 

 of that form. Still these differences, as may be seen from the figure 

 given on plate 5, seem to be of such a nature that they may be due to 

 different degrees of development in the specimens compared ; the few 

 individuals of A. eomplexus yet found, either at the original locality or 

 in New Jersey, being smaller than those of the form under consideration 

 with which 1 am comparing them. That first figured by Professor 

 Hall and the writer is not in a condition to give a clear idea of the septa 

 of the Kebraska shell. 



In the lobes and sinuses of its septa, this species is also very closely 

 allied to A. Gollevillensis, d'Orbigny {=A. Lewisiensis, d'Orb., not 

 Sowerby). It is a more gibbous shell, however, and differs in having 

 its costae developed entirely across to the inner side of its whorls, while 

 its periphery is completely destitute of the longitudinal groove so char- 

 acteristic of d'Orbigny's species. 



It is also nearly related to A. Egertonianus, Forbes, from the Creta- 

 ceous of India, but its volutions are less compressed, its costae smaller, 

 and its septa different in some of their details, particularly in the ar- 

 rangement of the small inner lobes near the umbilical margins. 



The largest specimen in the collection is from Sucia Islands. It is an 

 internal cast, and has its outer turn so much worn as to obliterate much 

 of the details of the lobes and sinuses, as may be seen by fig. 2 b of 

 plate 5. The inner turns, however, when separated, show the septa 

 very clearly. It consists entirely of septate whorls, the non-septate 

 portion having been broken away. In its greatest diameter, it measures 

 4.60 inches, and 1.90 inches in breadth. Others (retaining most of outer 

 chamber) measure about 3.15 inches in their greater diameter. 



Locality and position. — Komooks, Vancouver's Island, and at Sucia 

 Islands; Cretaceous. 



Genus PLACENTICERAS, Meek. 

 Placenticeras 1 Vancouvekense, Meek. 



Plate 6, fig. 1, 1 fl, 1 h, and 1 c. 



Amnoaiies Fancouverensis, Meek (18G1), Proceed. Acad. Nat. Sci. Phila., siii, 317. 



Shell discoidal ; volutions increasing rather gradually in size, strongly 

 compressed on the sides, and flattened on the narrow periphery, nearly 

 twice as broad from the peripheral to the umbilical side as the trans- 

 verse diameter, and rather deeply embracing; umbilicus of moderate 

 depth, and small, or rather less than half as wide as the greater diame- 

 ter of the outer whorl ; aperture (as nearly as can be determined from a 

 section of one of the whorls) compressed-subcordate. Surface orna- 

 mented by a row of compressed nodes along each margin of the peri- 

 phery, and another of smaller size around the umbilicus of each side ; 

 about twenty of the first and ten of the latter may be counted on each 

 side of an entire turn. The flattened sides between the peripheral and 

 umbilical rows of nodes are provided with obscure, slightly-arching, 

 transverse costae, one of which extends from each of the umbilical nodes 

 toward the peripheral margin; but all become obsolete before reaching' 

 it, at least on the outer turn. Between each two of these principal 



