82 CARBONICOLA, ANTIIRACOMYA, AND NAIADITES. 



Exterior. — The shell is ornamented with distinct but fine lines and stris9 of 

 growth somewhat oblique to the long axis of the shell. 



Dimensions. — Fig. 15, PI. XX, measures — 



Antero-posteriorly . . . .20 mm. 



Dorso-ventrally . . . .10 mm. 



Locality. — Lower Cement-stone series, Fife ; Limestone No. 10, at Rander- 

 stone, in a three-inch band of calcareous ironstone in light-grey sandy slate ; in 

 cliffs east of Pittenweem. 



Observations. — This species was described by Mr. Kirkby, in his careful and 

 accurate paper on the Marine Zones of the Calciferous Sandstone Series of the 

 Fifeshire coast, under the name of Pleurophorus elegans, the generic name being 

 given on the authority of Prof, de Koninck. He has kindly lent me a series of 

 his fossils for study, and I have been able to examine the hinges and casts of the 

 interior, with the result of coming to the conclusion that his shell belongs to the 

 genus Carbonicola. The form of the hinge is practically identical with the type 

 found in Carbonicola aquilina, and this differs markedly from the form found in 

 Pleurophorus, which King states (Palgeontographical Soc. vol. for year 1849, 

 "Permian Fossils," p. 180): "Cardinal teeth two in each valve, diverging 

 inwardly, and interlocking alternately ; posterior teeth linear." Moreover, the 

 species under discussion does not possess externally the radiating ribs on the 

 posterior slope nor the characteristic shape, wider in a dorso-ventral direction 

 posteriorly, which are to be seen in Pleurophorus. 



Carbonicola elegans possesses characters which also are found in the other 

 species which occurs in the Calciferous Sandstone Series, C. antiqua. The 

 bevelled inner edge of the posterior border and other hinge peculiarities are 

 similar in both, but there is no doubt that they are not the same species, differing 

 so markedly from each other in shape and form. 



Mr. Kirkby describes a faint diagonal ridge running from each umbo towards 

 the postero-ventral angle, which I have been unable to make out in any of the 

 specimens sent me, but otherwise his description is very accurate. 



The shell more closely resembles C. aquilina than any other species, having in 

 common with it the lines of growth arranged obliquely to the long axis of the 

 shell, and the upper border of the anterior end being much below the level of the 

 umbones ; also the hinge characters are very similar; but Carbonicola elegans is 

 more cylindrical, and has its umbones curved inwards, downwards, and forwards. 



In the same beds with C. elegans only one other Mollusc is found, Littorina 

 Scotoburdigalensis, but Leperditia Oheni, var. attenuata, and Cytherella also occur 

 — a very similar fauna to that which accompanies C. au.lif/n.a ; and it is very 

 noticeable that the typical marine forms so abundant in the other shell-beds of the 

 Fifeshire coast are conspicuously absent. With regard to the shell called 



