GEOLOGICAL SURVEY OF THE TEERITOEIES. 487 



face, four pairs of tliem forming two longitudinal rows along the gla- 

 bella, while the entire surface between these is very minutely granular 

 as in the last. 



There are also numerous other smaller specimens agreeing with the 

 last two, excepting that they show generally but the most feeble traces 

 of lateral furrows iu the glabella. 



It is possible that some of these specimens may differ specifically 

 from the type of the species here proposed, but I am at present inclined 

 to regard them all as only diiferent varieties and ages of the same. 



One of the specimens associated with the others consists of portions 

 of the cephalic shield crushed, and most of the thorax consisting of 

 twelve of the body segments. This shows the axial lobe to be nar- 

 rower than the lateral, quite convex, gradually tapering posteriorly, and 

 rather strongly defined by the dorsal furrows. The lateral lobes are 

 depressed, sloping outward from the middle, and composed of rather 

 strongly furrowed pleurae, the furrows extending straightoutward at right 

 angles to the axis. It does not show the form of the free ends of the 

 pleurse. Surface nearly smooth, or only very minutely granulated. 

 This specimen may or may not belong to the species here named. 



If the name Conocephalites should be retained, with the limits usually 

 allowed this group of trilobites, of course our species would have to be 

 called Conocephalites Gallatinensis. As Conocephalus, first proposed by 

 Dr. Barrande, had been previously used for a genus of insects, however, 

 andCordahad proposed the name Gonocoryphe before Dr. Barrande 

 changed his name to Co7iocep1iaUtes, it seems to me that Corda's name 

 will have to stand. It will also be observed that there are two strongly- 

 marked types included in the genus by Dr. Barrande. That is, one 

 without eyes, and having the facial sutures forming such very different 

 curves as to give the free and fixed cheeks, as well as the frontal limb, 

 entirely different outlines- and proportions from those of the other type, 

 which has well-developed eyes. The first of these groups is represented 

 by C. Sulzeri and the latter by C. striatus. Corda, however, sej)arated these 

 types into two distinct genera, placing C. Sulzeri in his genus Gonoco- 

 ryphe and G. striatus in his genus Ptyclioparia. I have not his work at 

 hand for reference, but I infer from Dr. Barrande's citations that the two 

 species mentioned were so arranged by Corda that they may each be 

 regarded as typical of one of these groups. If so, it certainly appears 

 that both of -his names ought to be retained, at least in a subgeneric 

 sense. In this case it will be observed that nearly all of the numerous 

 species hitherto described in this country would fall into the gr'oup 

 Ftychoparia, as they all, with perhaps the exception of G. Matthewi, 

 Hartt, and one or two others, seem to have been provided with well- 

 developed eyes, and agree in other respects generically with G. striatus. 

 Adopting this view, the name of my G. Kingii becomes G. {Ptychoparia) 

 Kingii, and so on through nearlj^ the whole list of American species yet 

 known. 



Locality and position. — East side of Gallatin Eiver, above Gallatin 

 City, Montana, Potsdam or Primordial Zone. 



CEETACEOUS FOEMS. 

 OsTEEA soLENiscus, Meek. 



Ostrea solenieeus, Meek, 1870 ; Hayden's Geological Report, Wyoming, &c., page 296, 



List Cretaceous species. 



Shell attaining a large size, becoming rather thick iu adult examples, 

 generally straight, greatly elongated, and comparatively A^ery narrow. 



