180 CARBONIFEROUS LAMELLIBRANCHIATA. 



M'Coy first pointed out the identity of the shells described by Fleming and 

 Phillips, in his work on the Carboniferous Fossils of Ireland. For some reason 

 or other d'Orbigny, in his ' Prodrome Pal.,' removed this species into the genus 

 Oypricardia, a reference which M'Coy points out to be erroneous on account of 

 the characteristic Nuculoid hinge. 



The t} r pe specimen in the Gilbertson Collection (Brit. Mus.) is labelled 

 " Mountain Limestone, Bolland." The condition and matrix of the specimen, 

 however, demonstrate conclusively that it was never embedded in limestone ; and 

 I have never yet seen this species from beds of the Carboniferous Limestone. It 

 generally occurs in shales or calcareous ironstones, and ranges from the Calciferous 

 Sandstone Series (Fife) to the Coal-measures (North Staffordshire). 



The figure given by Wardle (oj). cit.) evidently belongs to an entirely different 

 shell, and at present there is no evidence that this species occurs in the Car- 

 boniferous Limestone. 



De Ryckholt, speaking of the occurrence of Leda gibbosa in Belgium, says, 

 " Ce Leda presente en Belgique quelques varietes qui ne different, en general, de 

 la forme normale, que par une largeur moindre." The same author's Leda Sancti- 

 Adelini appears from the drawing to represent Fleming's species. De Koninck 

 considered the specimens referred to N. gibbosa by de Ryckholt, he did therefore 

 recognise them to be a distinct species. He says of Nucula pergibbosa, referring 

 to the difference between that form and N. gibbosa, " Elle s'en distingue, nean- 

 moins pas sa taille plus petit, par sa forme plus trapue, aussi que les ornaments de 

 sa surface." The Belgian specimens are certainly as a rule smaller than the 

 British ; but the description which de Koninck gives of the surface of his new 

 form, " garnie de plis concentriques d'acroissement peu reguliers surtout aux 

 environs du bord ventral," is characteristic of N. gibbosa, Fleming. 



Meek states in the ' Final Report on Nebraska,' p. 205, " After comparing 

 good specimens of N. ventricosa, Hall, from the Coal-measures of Illinois with 

 examples of a shell sent to Mr. Worthen .... from Carluke, Scotland, 

 with the name N. tumida, Phillips, attached, no satisfactory differences were 

 observed." I am, however, unable to agree with this opinion. There are 

 essential differences between a series of shells from Illinois, which I possess, and 

 N. gibbosa. The American shell is not so oblique, is regularly rounded in front, 

 with no lobe, sharper posteriorly, with a well-marked ridge passing down from 

 the umbo to the posterior border, marking off a broad ovate escutcheon. 

 Anteriorly, too, a slight curved ridge passes from the umbo to the anterior border, 

 forming a well-marked lunule. The shell is also much less swollen at the margins, 

 where it may be said to be compressed. I have figured a specimen of this shell, 

 PI. XIV, figs. 16 and 16a, for comparison. 



This species differs from all others of the genus by its short, regularly 



