cardinal angles ; dorsal valve very moderately concave or nearly flat. The surface is marked 
by from twenty to twenty-four simple, sub-angular ribs, some of which are occasionally bifur- 
cated towards the margin, and which are separated by interspaces wider than themselves. In 
the eared examples the ribs are obsolete towards the cardinal angles. ‘‘ The cardinal margin 
shows two and rarely three spines on each side of the cewtre, which are abruptly bent outwards - 
so as to lie nearly parallel to the hinge-line, and the outer one extending much beyond the 
cardinal extremity. The area is very narrow,” (Hall). 
we Some of the points mentioned in the above description I have 
not been able toverify from ourspecimens, as they are mostly imper- 
é fect. Thus, I have never seen either a dorsal valve, or a ventral 
valve exhibiting the spines. Upon the whole, however, I have no 
doubt but that our specimens are truly referable to C. mucronata, 
as they agree with Hall’s description of this species in all essential 
characters, so far as observed. As occurring in the Marcellus 
Shale, the ventral valve is stated by Hali as being only slightly 
convex or nearly flat; but as occurring in the Corniferous Lime- 
a. Chonetes mucronata, natural : oth cts 5 ; 9 
size, after Hall; a. The same en- Stone and Hamilton group, it is said to be “often quite gibbous. 
larged ; b. A specimen of C. mv- Qur examples agree with the latter in this, and only differ in hav- 
ercnata from the Corniferous . Z i 
Limestone of Ontario. Natural ing the cardinal angles more or less produced and salient—a phe- 
Lee nomenon, however, which Hall states to be of occasional ooeurrence. 
The species is nearly allied to Chonetes deflecta (Hall), and the two are, perhaps, only varieties 
of a single species. 
Locality and formation—Rather abundant in the Corniferous Limestone of Rama’s Farm, 
near Port Colborne. 
90. CHONETES HEMISPHERICA (HALL). 
Chonetes hemispherica (Hall), Tenth Report on the State Cabinet, p. 116. 
Chonetes hemispherica (Billings), Canadian Journal, New Series, Vol. VI. p. 349, Figs. 
121-123. 
Chonetes hemispherica (Hall), Pal. N. Y. Vol. IV. Pl. XX. Fig. 6. 
Shell semi-oval or semi-circular, the greatest width being along the hinge-line. Cardinal 
angles usually considerably produced and auriculate, sometimes reflected. Ventral valve very 
convex and ventricose, depressed in the neighbourhood of the ears, and sometimes showing a 
shallow mesial depression extending towards the front from the beak. Umbo very prominent, 
incurved, the area being often “inverted, or brought under the body of the shell at right 
angles to the plane of the margin” (Billings). The area has a width of about half a line, and 
is obliquely striated, whilst its outer margin carries the bases of from three to four small spines 
on each side of the umbo, which, however, appear to be very rarely preserved. Dorsal valve 
concave, following the ventral valve, but with a concavity less than the convexity of the latter. | 
Area of the dorsal valve narrow and almost linear, marked with a row of small transverse de- 
pressions or pits, which are most obvious near the umbo. 
Surface marked with radiating, rounded, simple ribs, which become obsolete on the ears. 
A few of the ribs bifureate. There are from four to five ribs in the space of one line, and 
they are separated by interspaces about equal to their own width. 
The dorsal valve of this species appears to be extremely rare, Hall having never observed 
it, and Billings having seen but two fragments. I have only come across a single specimen, 
which exhibits the interior. This example shows the cardinal process to consist of two nearly 
parallel and closely contiguous divisions, each of which is bifid at the tip. From the base 
of the cardinal process is continued a mesial ridge, which dies away towards the front of the 
shell ; and on either side of this are two diverging ridges which coalesce with the preceding at 
the base of the cardinal process. The radiating ribs are just as conspicuous in the interior as 
externally, and are marked by minute remote pustules arranged in a single row on each rib. 
The muscular impressions cannot be made out. 
Chonetes hemispherica is readily distinguished by its general form and its coarse stria- 
tion. The largest specimen I have seen appears to be about sixteen lines along the hinge-line 
by twelve lines in length ; but average examples are somewhat smaller than this. 
Locality and Formation.—Rare in the Cornifcrous Limestone of Port Colborne. (Also 
in the Schoharie Grit and Corniferous Limestone of the State of New York.) 
