520 DR WHEELTON HIND ON 



The umbones are tumid, subcentral, elevated, and moderately large. A large lunule and 

 escutcheon. 



Interior. — Hinge multidenticulate, anterior and posterior rows of teeth not con- 

 tinuous. Adductor muscle scars normal. In casts, the fossil is much cut away 

 posterior to the umbo, corresponding to the large escutcheon. 



Exterior. — The surface is adorned with numerous distinct, raised, parallel concentric 

 lines. 



Dimensions.— -Fig. 4, PI. IV., a right valve, measures : antero-posteriorly, 5 mm. ; 

 dorso-ventrally, 4 mm. 



Locality. — Scotland : Llandeilo beds, Ardmillan, Craighead, Balclatchie. Ireland : 

 Desertcreat, Co. Tyrone. 



Observations. — M'Coy should, I think, have preserved Portlock's varietal name, 

 instead of substituting a new one. Portlock, it was very evident, thought his species, 

 though very closely allied in form to Sowerby's Coal Measures form N. acuta, distinct. 

 He says : " Mr Sowerby's figures so closely agree with our specimen that it is difficult 

 to separate them ; still, however, it is probable that they are not the same." He then 

 proceeded to point out differences, and on that account gave the varietal name imbricata, 

 which I adopt on grounds of priority. The species has all the characters of the genus 

 Nuculana. The special concentric linear ornament is only found in this genus of the 

 Nuculidse in Carboniferous rocks. 



Nuculana concentrica, sp. nov. (PL IV., figs. 8, 9.) 



Specific Characters. — Shell small, transverse, deep anteriorly, narrowed posteriorly, 

 moderately compressed. The anterior margin bluntly rounded, the inferior gently 

 convex. The posterior border narrow, bluntly rounded. The hinge line arched, much 

 depressed posteriorly. The umbones small, erect, excavated posteriorly by the well- 

 marked dorsal slope and escutcheon, incurved, apparently directed backwards, subcentral. 

 The valves are gently swollen, with a very marked depressed, shallowed dorsal slope. 



Interior. — Hinge multidenticulate, but the cartilage fossa below the umbo has not 

 been seen. 



Exterior. — The surface is adorned with fine raised concentric lines, with sulci 

 between them of a width double that of the line. 



Dimensions. — Fig. 8, PI. IV., measures : antero-posteriorly, 13 mm. ; dorso-ventrally, 

 7 "5 mm. 



Locality. — Woodland Point, Middle Llandovery. 



Observations. — A well-marked species, which I have referred to Nuculana rather 

 than to Ctenodonta on account of its shape and ornament, and of the fact that there seems 

 to be a well-marked escutcheon. Three specimens, all from the same locality, are in the 

 collection, one of which shows both valves flattened out on a slab, the left valve being 

 somewhat crushed, but in the right valve the anterior part of the hinge plate is exposed. 



