162 CARBONIFEROUS LAMELLIBRANCHIATA. 



is the more important that it shows the hinge-plate with a large cardinal tooth 

 (Fig. 13 a). 



N. transversum is more transverse and has more radiating ribs of a finer and 

 closer character than N. radiatum. On account of these characters I have 

 established another species for Mr. Smith's shell. 



A smaller specimen was found by Mr. Dunn, of Redesdale, some years ago, 

 at the Coomb quarry, a locality which has yielded a rich fauna of the rarer 

 Carboniferous Limestone fossils. This agrees with Mr. Smith's specimen, which 

 has many fine radiating ribs, and is more transverse than N. radiatum. 



Family LUCINHLE. 



Genus Paracyclas, Rail, 1843. 



Paracyclas, Hall, 1843. Geol. Surv. N. York, Kef. 4th district, p. 171. 

 Lucina, Portlock, 1843. Rep. Geol. Londonderry, p. 571. 

 — M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 53. 

 Paractclas, Hall, 1885. Geol. Surv. N. York, Pal., vol. v, pt. 1, Laniell. ii, 

 p. xxxviii. 

 — Beushaiisen, 1895. Die Lamell. des Rheineschen Devon., p. 165 ; 



Abh. konigl. preuss. geol. Landes., n. s., pt. 17. 



Generic Characters. — " Shell equivalve, sub-equilateral, sub-orbicular or broadly 

 sub-elliptical. Anterior end regularly rounded; posterior end rounded or sub- 

 truncate, somewhat more produced below than the anterior. Beaks small and low, 

 generally rising little above the hinge-line. Hinge-line short. Post-cardinal slope 

 more or less defined by an oblique furrow or depression, which sometimes leaves 

 the extremity subalate. Surface concentrically striated, sometimes with strong 

 concentric ridges marking the exterior. Structure of hinge not fully observed. 

 Ligament supported on each side internally by a narrow plate, and leaving in the 

 cast two narrow grooves directed forward from the beak. Muscular impression in 

 the post-umbonal slope. Pallial line parallel with and a little within the margin of 

 the shell." 



Observations. — I have quoted Hall's diagnosis of the genus Paracyclas in its 

 entirety (pp. cit., 1885). Several species occur in the Devonian rocks of N. 

 America and Germany. Beushausen states that the hinge has two little teeth in 

 each valve under the umbo, and no lateral teeth. It is interesting to find the 

 genus persisting up to the Carboniferous Series. 



