298 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



43. Ammonites (Placentocerus) placenta. DeKay 7 : Fountain Creek, Colorado City. Cret 

 No. 4. 



44. Ammonites (Pleuroceras ?) serrato-carinatus, Meek 8 ; Medicine Bow Creek, 2. 



TEKTIAKY SPECIES. 



1. TJnio prise us, M. and H. 9 ; Limestone Hill, Bear Eiver City, and Parley's Park, 

 Utah, Gilmore, Wyoming. Eocene. 



2. TJnio Washdkeei, Meek (new species, description at end of list) ; Washakee, Henry's 

 Fork, Green Eiver, and on the latter stream, Wyoming. Eocene. 



3. TJnio Raydeni, Meek; between Grand and Green Eivers, Fort Bridger. 



4. TJnio iellinoides, Hall (?) (sp.) 10 ; Barrel Springs, Muddy Creek, Wyoming. 



5. TJnio Leanus, Meek (new species, see end of list) ; Church. Buttes, Henry's Fork, 

 Barrel Springs, and other localities in Wyoming. Miocene. 



6. TJnio (bvplodon?) belliplicatus, Meek; Parley's Park, Utah; Gilmore, Wyoming. 

 Eocene. 



7. Corbicula ( Yeloritina) Durlceei, Meek ; Bear Eiver City, Parley's Park, Utah, and 

 Gilmore, Wyoming. Eocene. 



8. Cyrena (Corbicula f) fracta, Meek (new species, see description); Hallville coal 

 mines. Eocene. 



9. Cyrena (Corbicula?) crassatelliformis, Meek (new species); Hallville coal mines. 

 Eocene. 



10. SpJiwrium (undetermined, perhaps 2 species) ; Elkton, Central Pacific railroad, 

 beyond Salt Lake. Miocene. 



11. Sphcerium (undetermined species) ; Barrel Springs, Wyoming. Miocene. 



12. Corbula (Anisorliynclius) pyriformis, Meek; Parley's Park, Limestone Hill, and 

 Bear Eiver City, Utah ; Gilmore, Wyoming. Eocene. 



Corbula (Anisorliynclius) pyriformis var. consentrica, Meek. 



13. Corbula (Anisorliynclius) Engelmanni, Meek; Limestone Hill and Sulphur Creek, 

 Utah. Eocene. 



14. Goniobasis Simpsoni, Meek ; Fort Bridger, divide between Muddy and Black Forks. 

 Miocene. 



15. Goniobasis tenera, Hall ? (sp.) u ; Barrel Springs, Wyoming. Miocene. 



rowly-truncated and flattened, or slightly-concave periphery, small umbilicus, &c. ; also in the much 

 more numerous lateral lobes of its septa, which increase in size to the third one inclusive, and thence be- 

 come gradually and regularly smaller to the umbilicus. It probably includes several cretaceous species. 

 In the same way, Ammonites lobatus of Tuoiney may be regarded as the type of another group, differ- 

 ing from Placentocerus in having the periphery sharply cuneate ah around, and the sinuses or saddles 

 between its numerous lateral lobes (which agree in number and proportional size with those in Placen- 

 tocerus), presenting very curious obtusely -lobed or uniform outlines. For this type I would propose the 

 name Sphenodiscus, in allusion to its sharply-cuneate periphery. 



8. This is not a true Ammonite, according to the latest classifications of this group of Cephalopoda, but 

 it is more nearly allied to some of the forms included by Mr. Hyatt in his group Pluroceras. Indeed, al- 

 though unquestionably a cretaceous species, I cannot see'how it can be properly placed in a distinct group 

 from the middle liassic species A. spinatus, Brug., which Mr. Hyatt includes in Pluroceras, since it 

 seems only to differ specifically from that form in having its keel more prominent, and another series of 

 obscure nodes on the costse at their inner ends, with a few smaller intermediate costs, generally with- 

 out nodes, between the larger nodiferous ones. If, however, there is anything in the development of 

 these shells that would place them in different groups, the cretaceous group, including the form under 

 consideration, might be appropriately termed Prionocyclus, and would include A. percarinatus, H. and M., 

 and A. Wooljari, of the English gray chalk. 



9. I am led to think, from the comparison of more extensive collections that have come in since I pro- 

 posed the name TJnio vetustus for one of the Utah forms, that it is only a more depressed variety of 77. 

 priscus, M. and H. 



10. It is with considerable doubt that I refer this shell to TJ.tellinoides (=Mya tellinoides, Hall, in Fre- 

 mont's Eeport, PL ill, tigs. 1 and 2), the mature specimens being generally three or four times as large 

 as that represented by Prof. Hall's larger figure, and proportionally less depressed, with the posterior 

 margin more broadly rounded or subtruncated. Still, by following the lines of growth, it may be seen 

 that when the shell had only attained the same size as that figured by Prof. Hall, it must have pre- 

 sented a very similar outline. Ebne of them, however; seem to have the beaks so nearly central, or 

 quite so elevated, as represented by his Figure 2, which may have been drawn from a distinct species 

 from that represented by Figure 1. ..-.-'. 



Our specimens are generally rather thin, somewhat compressed, longitudinally ovate in form, with 

 one rather oblique cardinal tooth in the right valve, and one or two smaller ones in the left. The lat- 

 eral teeth are long, a little arched, and consist of one in the right and two in the left valve. The sur- 

 face only shows lines of growth, and. some traces of a few very small longitudinal wrinkles near the im- 

 mediate'points of the beaks, which are rather depressed, and placed about one-third the length of the 

 valves from the anterior end. Should this form be found to be distinct from that named by Prof. Hall, 

 it may be called XT. subcompressus. 



It may be proper to remark here, that nearly or quite all of the shells figured by Prof. Hall, on PL 

 LTI of Fremont's Eeport, although there referred to marine genera, are really, as suspected by him, 

 fresh-water types. 



11 This is probably the Cerithium tenerum, Hall (see Fremont's Eeport), and is a true Goniobasis. In a 

 genus like this, however, containing so many closely-allied species, it is scarcely possible to identify, 

 with confidence, a form only known from a three or four-line description and figures of imperfect speci- 

 mens. At one time I had supposed the species, for which I have here proposed the name O. chrysalis, 

 to be the tenera. But specimens of the form I have above referred doubtfully to that species, having 

 been brought in from that region among the later collections, I find, on comparison, that they agree more 

 nearly in most respects with the figures and description of the species tenera ; while, at the same time, 

 jhey are clearly distinct .from that IJiad at first supposed to be the tenera, and hold a much higher posi- 

 f 



