518 DR WHEELTON HIND ON 



Scotch specimens agree better with the description than the figures. Whether the 

 genus is correctly stated as Ctenodonta I doubt, but in the absence of definite knowledge 

 I can only say that the shape and general character of the shell would lead me to 

 suggest Nucula. The species is not uncommon. 



Nucula? varicosa, Salter, 1854. (PL III., figs. 32-37.) 



Nucula varicosa, Salter, 1854, Q.J.G.S., vol. x. p. 75. 

 Ctenodonta varicosa, Salter, Siluria, 2nd ed., p. 213, fig. 4. 



„ „ ,, 1866, Mem. Geol. Surv. Ot. Britain, vol. iii. p. 345, Woodcut xiii. 



fig. 1. 



Specific Characters. — Shell obliquely and triangularly ovate, gibbose. Umbones 

 subcentral, raised, incurved, and somewhat prosogyrous. The cardinal margin is sub- 

 angular, the inferior bluntly rounded. 



Interior. — The anterior adductor scar is deep and rounded, placed some way within 

 the margin and half-way down ; the posterior is rounded and placed low down. The 

 hinge plate is multidenticulate, but I am unable to say whether there is a fossa between 

 the anterior and posterior rows of teeth. 



Exterior. — The surface is almost smooth ; but towards the lower margin are some 

 deep, distant, concentric lines. 



Dimensions. — Fig. 32, PI. III., measures : antero-posteriorly, 10 mm. ; dorso-ven- 

 trally, 9 mm. 



Localities. — Scotland : Llandeilo series at Ardmillan and Dowhill. England : Caradoc 

 beds, Onny River, Bala, Conway Falls, Horderly. 



Observations. — I am unable to decide whether this species should be referred to 

 Nucula or Ctenodonta. The shape and general characters of the shell incline me to 

 adopt Salter's first view and to retain the species in Nucula. Ctenodonta, as far as I 

 know from a study of the Carboniferous species, never assumes the peculiar shape of 

 the species under discussion. 



Genus Nuculana, Link., 1807. 

 For synonymy, vide Hind, 1897, Mono. Brit. Carb. Lamell. (Pal. Soc.), p. 192. 



Generic Characters. — Shell transverse, more or less narrowed behind and produced 

 into a beak. Ombones small and contiguous ; lunule and escutcheon well marked. 

 Cardinal border somewhat angular. Hinge teeth numerous, in two sets, which do not 

 extend very far on each side of the umbo, separated by a fossa for the ligament, which 

 is internal, placed between the anterior and posterior sets of teeth. Posterior slope 

 more or less keeled. Pallial line sinuated or not. Surface ornamented with fine, 

 regular, concentric, parallel grooves and lines. 



Observations. — The generic characters are quoted from my monograph on the 

 Carboniferous lamellibranchs (op. supra cit.). It is interesting to find specimens of the 



