1874.1 33 [Allen. 



Dactylioceras anmilatum. 



A form allied to this species appears in Fraas' collection under the 

 name of Amm. annulatus triplicates Quenst., in the Macrocephalibed. 

 This form is precisely intermediate between the true annulatum and 

 the Amm. athleta of the upper formations, and as stated by him it 

 is not the same as the annulatus of the Upper Lias, though very 

 closely allied to it. It is also distinct from athleta, and other allied 

 forms of the same group, in which the adults acquire the spines and 

 peculiar outlines of the abdomen and septa of the athleta group. 



June 3, 1874. 

 Prof. Hyatt in the chair. Thirty-one persons present. 

 The following paper was read : — 



Notes on the Natural History of Portions of Dakota 

 and Montana Territories, being the Substance of a 

 Eeport to the Secretary of War on the Collections 

 made by the north pacific railroad expedition of 

 1873, Gen. D. S. Stanley, Commander. By J. A. Allen, 

 Naturalist of the Expedition. 



I. Introductory. 



The route taken by the Expedition may be briefly indicated as fol- 

 lows : — Starting from Fort Rice, on the Missouri River (a point a 

 little to the north of the geographical centre of Dakota), our course 

 was thence nearly due west to the Yellowstone River, in Montana 

 Territory, which we struck a few miles above the mouth of Glendive 

 Creek. Crossing the Yellowstone at this point, (where a temporary 

 post was established, called Camp Thorne), we followed up its left 

 bank to Pompey's Pillar, a distance of one hundred and ninety miles. 

 We kept mainly to the bottom lands, but the high bluffs being cut by 

 the river at frequent intervals, we were forced occasionally to tne 

 adjoining highlands. Leaving the Yellowstone at Pompey's Pillar, 

 we crossed over to the Musselshell, which we struck near the 109th 

 meridian. From this point the Expedition descended the valley of 

 the Musselshell, as far as the " Big Bend," — a distance of about sev- 

 enty miles — where we left it, and by a southeasterly course reached 



PROCEEDINGS B. S. N. H. — VOL. XVII. 3 OCTOBER, 1874. 



