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 urnbo. The surface is marked by fine, sub- 

 equal, usually rounded, radiating stripe, those near the margin often alternating in size. There 

 are about six of the larger striae in the space of one line, and there are between fifty and 

 sixty striseat 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 concentric 

 striae are also visible. 



This pretty little species occurs quite com- 

 monly in the decomposed shales uf the Hamilton 

 group at Widder, generally in a state of beauti- 

 ful preservation. It is nearly alied to Chum to 

 lineata,ihe most satisfactory distinction seeming 

 Fig. 23. to be that the dorsal valve is much more deeply 



a. chonetu i scitula, Haii natural size. 6 Area of the concave than in the latter species, whilst the 



same, enlarged, c. Chonetes lepida, Hall, natural size, c. . ... 



The same enlarged. All from the Hamilton group. Stri33 are more prominent. C. SC'ltUta IS alSO' 



very nearly related to C. lepida (Kail), and I should doubt if the latter is truly more than the 

 young of the former. The chief character relied upon to separate these species is that C. 

 scitula has the ventral valve uniformly convex, whilst there is a mesial depression in that of 

 C. Ityida. I have, however, specimens in other respects entirely agreeing with C. scitula, but with 

 a slight mesial sinus of the ventral valve. Nevertheless, in deference to the authority of the 

 great American palaeontologist, 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, PI. XXI., 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 striae 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 stride on the margin is only about twenty four or twenty- 

 five ; but smaller striae 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 G. Lf[>ida are very small shells of almost hemis- 

 pheric form, and one of the characteristics is the mesial depression of the ventral valve. The 

 striae are rather strong, angular, and, from dividing below, have the appearance of being fasci- 

 culate. More extensive collections have brought together a large number of individuals ; and 



~ O o ' 



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. sdtula, but the well-marked specimens of this 

 species have a convexity which precludes them from acquiring by growth the form and con- 

 vexity of 0. scitula in its characteristic phases," (Pal. A. 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, ^fh 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., PI. XX., fig. 1, and PL XXI., 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 



