CTENODONTA SINUOSA. 211 



times as many as twenty-four, situated with their angles pointing forwards, and 

 becoming gradually smaller as they approach the umbo, where they are very minute 

 and crowded. There is no gap between the two sets, or any internal socket for the 

 cartilage. The umbones are much hollowed out, so that casts of them are 

 acutely pointed, much more so than the shell itself. The pallial line is entire and 

 inconspicuous. 



Exterior. — The surface is ornamented with numerous regular concentric lines, 

 separated by bands of very fine striae. 



Dimensions. — Fig. 2, PI. XVIII, a cast, measures — 



Antero-posteriorly . . . .17 mm. 



Dorso-ventrally . . . .12 mm. 



Laterally . . . . .8 mm. 



Locality. — England : in Calcareous Bullions and Shale below the Third Mill- 

 stone-grit, Congleton Edge, Cheshire. 



Observations. — This species was described by de Ryckholt as Leila, and sub- 

 sequently by de Koninck as Tellinomya sinuosa. I have examined the specimens 

 in the type collection at the Royal Natural History Museum, Brussels, and have 

 no doubt as to the identity of the British specimens. I have been fortunate enough 

 to obtain some beautiful impressions of the hinge-teeth in casts, one of which I 

 figure, PI. XVIII, fig. 1 a, which at once shows the absence of the cartilage-pit 

 between the anterior and posterior sets of teeth, which is present in all the 

 Carboniferous species of Nucula and Nuculana. 



Externally the species somewhat resembles Nucula Isevirostrum, PI. XV, figs. 

 34 — 38, but I think that I have satisfied myself of the presence of the internal 

 cartilage-pit in this species ; nor does it possess the escutcheon, in the anterior 

 part of which probably was lodged the external ligament which is said to be 

 present in G. sinuosa. 



De Koninck states that his specimens were obtained from the " calschiste " 

 of Tournai, which is considered to be near the base of the Carboniferous rocks of 

 Belgium. My specimens, curiously, are from an horizon presumably far higher, 

 occurring as they do in calcareous shales some little distance below the Third 

 Millstone-grit, the Fourth and Fifth grits not extending so far south, but 

 dying out a few miles north of Congleton Edge. The fossiliferous bed is situated 

 upon a thick bed of quartzose, gannister-like sandstone with plant remains, and 

 has been described at p. 93 of this Monograph ; though the present species is 

 not included in the list, having been only obtained, with several other species 

 new to the horizon, since that part of the work was published. I cannot see any 

 real difference between G. Halli of Barrois and G. sinuosa. Though de Koninck 

 says (p. 139), " La Tellinomya {Gtenoilonta) Halli, C. Barrois, du terrain carbonifere 

 d'Espagne, est a peu pres la seule espece de cette formation qui ait une certaine 



