120 Prof. S. A. Nicholson — New Devonian Fossils. 



Locality and Formation. — Very abundant in certain beds of the 

 Corniferous Limestone at Port Colborne and Hagersville. 



Genus Letorhtnchus, Hall. 



" The shells of this genus are ovate, circular, or transverse, with 

 valves unequally convex, and marked by a median sinus and fold in 

 the ventral and dorsal valves respectively. The surface is plicated 

 by rounded bifurcating plications, vphich are always more conspicuous 

 on the mesial fold and sinus, whilst they often become obsolete on 

 the lateral portions of the shell ; concentrically marked by strong 

 lines of growth. Substance of the shell fibrous, usually thin. Yalves 

 articulating by teeth and sockets ; the apex of the ventral valve 

 perforate at some period of its growth, the lower side being com- 

 pleted by deltidial plates. On the interior of the ventral valve, 

 two short diverging dental lamellas extend into and are joined to the 

 sides or bottom of the rostral cavity : the muscular impression occu- 

 pies a narrow triangular or ovate-triangular space below the dental 

 lamellse. The dorsal valve has a well-defined septum, often reach- 

 ing below the middle of the valve, and divided above, leaving a 

 triangular or s]30on-shaped depression. The hinge-plates are narrow 

 strong processes with sockets embracing the teeth of the opposite 

 valve." (Hall, Pal. N. Y. vol. iv. p. 355.) 



I am not in the position to pronounce any opinion as to the validity 

 of the genus Leiorhynchus, or as to the propriety of separating it 

 from EhyncJionella, to which it is certainly most closely allied. In 

 the meanwhile, as Hall has described under this title several species 

 from the Hamilton and Chemung formations, I shall accept the genus 

 for the reception of two forms which occur in the Hamilton Group 

 of Ontario, one of them being the previously recorded L. multicosta, 

 Hall {■=^Bhynchonellal Laura, Billings), and the other being new. 



Leiorhynchus Huronensis, Nicholson, PI. YI. Fig. 11. 



Shell elongate-ovate, the greatest width being from one-sixth to 

 nearly one-fifth less than the length, whilst the greatest width is 

 placed nearly about the middle of the shell. Ventral valve convex, 

 .very gibbous in the umbonal region, abruptly curving to the sides, 

 and depressed from about the middle to the front margin of the 

 shell. A very broad and exceedingly shallow mesial sinus, which is 

 obsolete near the beak, but occupies almost all the front margin of 

 the shell, and supports about five low rounded plications. Beak of 

 the ventral valve large, prominent, and incurved, apparently not 

 perforated by a foramen, in close contact with the umbo of the dorsal 

 valve. Dorsal valve convex, strongly curved towards the sid'es, its 

 centre occupied by a broad mesial fold, which corresponds with the 

 ventral sinus, and carries five rounded plications. Margins of the 

 fold and sinus more or less distinctly interlocking. Beak of the 

 dorsal valve deeply buried beneath that of the ventral valve. Surface 

 marked with rounded plications, which are very obscure except upon 

 the fold and sinus, and which become nearly or quite obsolete in the 

 neighbourhood of the beaks. The plications are crossed with very 

 fine concentric strise, and with strong and very well-marked lines of 



