— —— 
of the ventral. The cardinal margin of the ventral valve generally shews very distinctly the 
bases of five tubular spines on each side of the umbo. The surface is marked by fine, sub- 
equal, usually rounded, radiating strie, those near the margin often alternating in size. There: 
are about six of the larger striz in the space of one line, and there are between fifty and 
sixty striee at the margin of the shell, the increase in proceeding from the beak being effected 
partly by bifurcation and partly by intercalation. In well preserved specimens fine concentri¢ 
strize are also visible. 
This pretty little species occurs quite com- 
monly in the decomposed shales of the Hamilton 
group at Widder, generally in a state of beauti- 
ful preservation. It is nearly alied to Chonetes 
lineata,the most satisfactory distinction seeming 
Fig. 23.00 ___ to be that the dorsal valve is much more deeply 
eel red. a. Chencie tires eta Sanat tie ne COR GRNE than in the latter SP Clee whilst the 
The same enlarged. All from the Hamilton group. striz are more prominent, Oe scitula 18 also 
very nearly related to C. lepida (Hall), and I should doubt if the latter is truly more than the 
young of the former. he chief character relied upon to separate these species is that (. 
scitula has the ventral valve uniformly convex, whilst there is a mesial depression in that of 
C’. lepida. I have, however, specimens in other respects entirely agreeing with’. scitula, but with 
a slight mesial sinus of the ventral valve. Nevertheless, in deference to the authority of the 
great American palzontologist, I shall in the meanwhile retain C. lepida as a distinct species. 
Locality and formation.—Common in the Hamilton Formation of Widder, in the ‘Town- 
ship of Bosanquet. 
88. CHONETES LEPIDA (Hall). 
Chonetes lepida (Hall), Tenth Report on the State Cabinet, p. 148. 
Chonetes lepida (Hall), Pal. N. Y., Vol. IV., p. 132, Pl. XXTI., fig. 5. 
The shell in this species in all essential respects agrees with that of C. scitula (Hall), and 
the following may be noted as the only points of distinction :— 
1. The form of the shell is sometimes nearly hemispherical, and the width of the hinge- 
line equals that of the shell below. 
2. The gibbous ventral valve exhibits a longitudinal mesial depression, bounded on each 
side by strize rather larger and more prominent than the rest. 
3. The hinge-line usually exhibits the bases of two or three spines on each side of the 
beak, but as many as five on each side can sometimes be detected. 
4. The number of the radiating strize on the margin is only about twenty four or twenty- 
five ; but smaller strize are sometimes intercalated between these, raising the total number to 
about fifty. 
As before stated, my own impression is, that Chonetes lepida is the young of C. scitula. 
Upon this subject, however, Prof. Hall has the following remarks :— 
‘“ The original specimens designated as (. /epida are very small shells of almost hemis- 
pheric form, and one of the characteristics is the mesial depression of the ventral valve. The 
strize are rather strong, angular, and, from dividing below, have the appearance of being fasci- 
culate. More extensive collections have brought together a largenumber of individuals ; and 
while the characteristic features are preserved in most of the specimens, there are others of the 
same size which seem like the young of C. svi/wia, but the well-marked specimens of this 
species have a convexity which precludes them from acquiring by growth the form and con- 
vexity of C. scitula in its characteristic phases,” (Pal. V. Y. Vol. IV., p. 133). 
Locality and formation.—Small specimens having the characters ascribed to C. lepida 
are not uncommon in the decomposed shales of the Hamilton group, at Widder, Township of 
Bosanquet. 
89. CHONETES MUCRONATA (Hall). 
Strophomena mucronata (Hall), Geol. Report, 4th District, New York, p. 180, fig. 3. 
Chonetes laticosta (Hall), Tenth Report on the State Cabinet, p. 119. 
Chonetes mucronata (Hall), Pal. N. Y., Vol. IV., Pl. XX., fig. 1, and Pl. XXTI., fig. 1. 
Shell small, semi-oval, or more or less auriculate, the hinge-line equal to or greater than 
the greatest width of the shell below. Ventral valve strongly convex, depressed towards the 
