2() GEOLOGICAL SURVEY OF THE TERRITORIES. 
Genus CYRENA Lamarck. 
CYRENA CARLETONI Meek. 
Plate 12, figs. 16 a and 6b. 
Cyrena carletoni Meek, 1873, An. Rep., U. 8. Geol. Sur. Terr. for 1872, p. 495. 
The following is Mr. Meek’s description of this interesting species, 
together with his remarks upon it: 
“Shell small, thin, subeircular or with length a little greater than the 
height, moderately convex; anterior and posterior margins rounded from 
above "regularly into the Younded basal outline, or with the posterior 
sometimes slightly straightened, both rounding more abruptly to the 
hinge above; beaks rather depressed, small, abruptly pointed, incurved, 
nearly contiguous, and placed slightly in advance of the middle; hinge 
line sloping very eradually from the beaks. Surface marked with 
moderately distinct concentric lines and furrows. 
‘‘Length of a medium-sized specimen, 0.55 inch; height of same, 0.49 
inch; convexity, 0.52 inch. 
“This shell is so very thin, and so nearly resembles a rather large 
Spherium in form and surface characters that I certainly should have 
referred it to that genus had not a lucky blow separated the hinge of a 
right valve from the matrix in such a manner as to expose the teeth 
quite satisfactorily. This shows its hinge to have the characters of a 
true Cyrena. For so thin a shell it has quite a stout hinge. Its cardinal 
teeth are rather diverging, the posterior two being well developed, and 
each a little furrowed along the middle, while the anterior one (in this 
right valve) is much smaller and conical in form. The lateral teeth are 
of moderate size, and certainly smooth, the posterior being remote from 
the cardinal teeth, and the linear anterior extending back to the latter. 
Internal casts show the muscular and pallial impressions to be well de- 
fined, and the latter to be a little straightened, or showing a very faint 
tendency to form a small sinus under the posteri i0r (adductor scar). 
“This is a rather small and an unusually thin shell for the genus Cyrena, 
being, as already remarked, much more like a Spheriwm in these char- 
acteristics. It is quite abundant at the locality, but, as it is only found 
in an indurated clay matrix, good specimens are with difficulty obtained, 
and from these the thin shell is very liable to break and scale oif, leav- 
ing only the internal cast remaining. 
‘Among the specimens collected there are some of a more transversely 
oval form and somewhat larger size than those I have regarded as the 
types of the species here described. These may belong to a distinct 
species, but they agree so nearly in all other known characters that I 
am at present inclined to regard them as merely a variety of the same. 
Locality and position. —Carleton’s coal mine, Coalville, Utah.” 
This species is one of an interesting estuary fauna ’ which was (is- 
covered by Mr. Meek in connection with a portion of the coal-bearing 
strata in the Cretaceous series at Coalville, Utah. The figures on plate 
12 have been drawn from his types, which are among the only examples 
that have ever been collected. 
One of the species of this peculiar estuary fauna, namely, Physa carle- 
toni, was illustrated on plate 7, fig. 12, of Contributions to Invertebrate 
Paleontology No. 1, in the Annual Report of the Survey for 1877, and all 
the remaining species of that estuary fauna which have yet been deseribed 
are illustr ated upon plate 12 of this article. They embrace the following 
