"6 



91. CHONETES ARCUATA (Hall). 



Chonetes arcuata (Hall), Tenth Report on the State Cabinet, 116. 

 Chonetes arcuata (Hall), Pal. New York. Vol. IV., Plate XX., Fig. 7. 



Shell semi-elliptical, or nearly semi-circular; the hinge line equal to, or slightly longer 

 than, the greatest width of the shell; the cardinal angles produced into distinct ears, which, 

 however, are usually short and compressed. 



Ventral valve extremely convex or ventricose, often with a shallow longitudinal depres- 

 sion, extending from the umbo to near the middle of the shell. Beak prominent and in- 

 curved ; hinge-line supporting ten to twelve tubular spines, which are directed obliquely out- 

 wards, and are rarely preserved. Dorsal valve deeply concave, following the convexity of the 

 ventral valve. 



Surface marked by fine rounded striae, which both bifurcate and increase by interstitial 

 addition. From six to seven strife occupy the space of one line, and the intervals between 

 them are not only narrower than the width of the ribs themselves, but often have the charac- 

 ter, especially in partially exfoliated specimens, rather of rows of elongated pits than of dis- 

 tinct grooves. 



This species is very closely allied to C. hemispherica in its form and general character. 

 It is readily distinguished from the latter by its much more numerous and finer striae. 



Locality and Formation. Not uncommon in the Corniferous Limestone of Port Colborne. 



92. CHONETES ACUTI-RADIATA (Hall). 



Strophomena acuti-radiata (Hall), Geol. Report, 4th Dist., New York, p. 171, 

 Chonetes acuti-radiata (Hall), Tenth Report on the State Cabinet, p. 117. 

 Chonetes acuti-radiata (Hall), Pal. N.Y., Vol. IV., Plate XX., Fig. 5. 



Shell semi-elliptical, it width along the hinge-line nearly or more than twice as great as 

 Its length ; cardinal angles produced. 



Ventral valve convex, but not excessively so, depressed towards the flattened ears, some- 

 times abruptly arched or bent downwards from the middle towards the margin, so that the 

 marginal portion of the shell forms nearly a right angle with the umbonal region. Sometimes 

 a slight mesial furrow or depression, extending from the beak to the front margin. Dorsal 

 valve, characters of the area, and interior markings' unknown. Surface marked by sub-equal, 

 rounded, or sub-angular radiating ribs, about six in the space of one line, which increase by 

 bifurcation and interstitial addition in proceeding from the beak to the margin. On the car- 

 dinal extremities the ribs are faintly marked, or obsolete. 



According to Hall, the hinge-line carries, 

 on each side of the umbo, four or five 

 strong tubular spines, which are obliquely 

 directed outwards ; but no traces of these 

 are preserved in the few specimens col- 

 lected by me. C. acuti-radiata is nearly 

 Fig. 25. allied to both C. hemispherica and C. arcv- 



a, Ventral valve of Chonetes acitti-radiata (Hall), natural size ata ; but it is distinguished by the dis- 

 (after Hall) ;b, Ventral valve of another specimen of the same from m :j4V. f *U c,V,ll nl/vn +1,/ 



the Corniferous Limestone of Ontario, natural size. _ proportionate Width Ot the Shell along the 



hinge-line as compared with the length, the flattening of the cardinal extremities, and the less 

 convexity of the ventral valve. The striation is also finer than it is in S. hemispherica. 

 Locally and Formation. Rare in the Corniferous Limestone of Port Colborne. 



Genus PRODUCTELLA (Hall). 



" Shells having the general form of Productus, but uniformly with a narrow area on each 

 valve, a foramen or callosity on the ventral area, small teeth, and more or less distinct teeth- 

 sockets. The reniform vascular impression, rising from between the anterior and posterior 

 occlnsor muscular impressions, curves gently outwards, and following a curvature somewhat 

 parallel with the margin of the shell to below the middle of its length, is abruptly recurved, 

 and the extremity, turned a little backwards, terminates about half way between the margin 



