112 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Genus MEEKOCERAS* Hyatt. 
“These species, so far as they go, are unlike the Ceratites of any for- 
eign locality, but have more resemblance to the Muschelkalk than to 
the St. Cassian or Hallstadt faunas. They possess in common one 
characteristic which separates every species from the typical forms of 
European Ceratites. There are but three distinct lateral cells and two 
lateral lobes besides the finer auxiliary lobes and cells. This occurs in 
the most involute species, ‘C’ [M. gracitétatis], as well as in the least in- 
volute [M. aplanatum]. This characteristic would be of no small value 
in any group, but in this one it is unusually constant.in spite of the 
great differences of form and the variations in breadth of the sides of 
the whorls between the different species. The typical Ceratites. the C. 
nodosus and .C. semipartitus have at least four distinct lateral cells and 
lobes besides the auxiliary ones, and the distinction is slight between 
the two series. In this genus, on the contrary, the auxiliary series, 
when present, is not divided from the third lateral cell by a distinct lobe 
as in Ceratites, and the aspect of the third lateral cell is often like that 
of a Goniatites. The auxiliary series is of course not present in the less 
involute and narrower sided forms, such as ‘A’ [M. aplanatum], and Ami. 
parcus, Amm. boydanus, and Amm. ottonis, as figured by von Buch; and 
Ceratites carbonarius Waagen. These and the Goniatites levidorsatus 
Gabb (which I have in Meek’s report on the Paleontology of the Geol. 
Expl. 40th Parallel, erroneously referred to Clydonites), are quite distinct, 
but the adult sutures of the latter are not known, and its position is there- 
tore uncertain. : 
‘The compressed whorls of all the species is of course a characteristic 
which is obvious when they are contrasted with typical Ceratites, as is 
also the absence or merely transient appearance of heavy nodes or ribs, 
except, perhaps, in the least involute species, if levidorsatus be found to 
belong to this genus. The young shel)s appear to be quite distinct from 
the young shells of true Ceratites, so far as these have been compared, 
though no exact observations could be made for want of good specimens 
of the young of the true Ceratites..—(A. H.) 
MEEKOCERAS APLANTUM White. 
Plate 31, figs. 1 a, b, ec, and d. 
Meekoceras aplanatum White, 1879, Bull. U. S. Geol. Sur. Terr., vol. v, p. 112. 
Shell compressed, discoidal, having the peripheral or siphonal side of 
the outer volution flattened, that of the inner volution being a little 
rounded, and although narrow, its breadth is considerable as compared 
with the small transverse diameter of the volutions ; umbilicus open, shal- 
low, its width in the adult being about equal to that of the greatest verti- 
cal diameter of the outer volution, but it appears to have been propor- 
tionally wider in young examples; volutions flattened, convex on their 
sides, but their inner edges are abruptly rounded inward to meet the 
next volution; all the volutions slightly embracing; the inner ones some- | 
what less so than the outer. Siphonal cell of the septa small, and upon 
the inner volutions it is very small; in the outer septa it occupies the 
whole width of the flattened portion of the periphery, bringing the small 
outer lobes upon the angle between the sides and the fattened periphery ; 
outer and middle cells of nearly the same width, the outer regularly, and — 
* “Dedicated to the memory of my friend, F. B. Meek, as some slight testimony of 
my respect for his works and regret for his loss.”—[A. H.] 
