96 CARBONIFEROUS LAMELLIBRANCHIATA. 



cle VeraeuiTs species, showing his view of the matter. A. inter stitialis has much 

 the same general characters as A. Murchisoni; the latter is, however, easily 

 distinguished by possessing a single fine rib between each pair of strong ones in 

 the left valve. M'Coy's very accurate description under the name A. segregatus is 

 perhaps a little too exact with regard to the number of strong ribs, and also of the 

 finer ones between them. The number varies with the growth of the valve ; in very 

 large examples there may be as many as five secondary ribs in the broadest spaces, 

 which are the fifth and sixth from the anterior end. 



I have no hesitation whatever in placing Limatulina selecta, de Koninck, as a 

 synonym of M'Coy's shell. De Koninck figures both valves, and describes the 

 peculiar character of the external surface of the right valve. 



Although, unfortunately, the type of Pecten interstitialis has disappeared, and 

 the figure is quite unrecognisable, yet Phillips's description is sufficiently definite to 

 leave no doubt as to the real character of the shell. The original description is as 

 follows: — "With about sixteen narrow, sharp, rough, radiating ribs, the intervening 

 spaces with three striae or finer ribs. A specimen in Mr. Gilbertson's collection 

 has stronger ribs. Near the beak the ribs are alternately larger and smaller, ears 

 acute." M'Coy retained Phillips's species, but unfortunately gave no illustrations, 

 in his second account. In his ' Brit. Pal. Foss.,' page 48, however, he evidently 

 describes a different shell. He states that this form possesses nine to eighteen 

 narrow, sharp, radiating ribs, between which are three to nine smaller, and that the 

 ribs have hooked spines at close regular intervals, and he makes Pecten inter xostatus 

 a synonym of Phillips's P. interstitialis. I think M'Coy was in error as to the true 

 characters of Phillips's V. interstitialis. In the account of A. segregatns M'Coy 

 draws attention to the distribution of the radiating ribs of the left valve as follows : — 

 " Surface radiated with about six strong, narrow, obscurely rugged ridges, between 

 each pair of which are three smaller, the middle one largest and alone extending 

 to the beaks along with the six primary ridges, which they there nearly equal in 

 size." This account is practically identical with that of Phillips. M'Coy's type 

 specimen is so crushed and so faint as to be scarcely recognisable ; I do not propose 

 to reproduce it. De Koninck's Aviculopecten interstitialis is quite different from 

 Phillips's species ; the surface is stated to be " ornamented with radiating ribs, 

 alternately thick and thin." This author draws attention to the fact that M'Coy 

 lias quite mistaken the shell; a fragment in the Gilbertson Collection labelled 

 Pecten interstitialis should be referred to A. Murchisoni, M'Coy. De Koninck 

 thinks it improbable that P. Kohcharqfi and P. Bouei, de Verneuil, can be the same 

 species. He considers the former a Permian and the latter a Carboniferous shell. 

 Eichwald, however, who would have had more experience of Russian specimens, and 

 probably access to the types, considered the two species as identical. De Koninck 

 says : — " P. Kolccharuji, de Vera., has a more pronounced shape, and the ribs on 



