NAIADITES CARINATA. 139 



Interior. — The arrangement of muscle-scars, and the hinge-line, differ in no way 

 from the descriptions given under No indites modiolaris, except that the posterior 

 adductor scar is circular, and is situated just on the slope of the ridge about half- 

 way down the shell. 



Exterior. — The markings are precisely similar in character and arrangement 

 to those which obtain in the preceding species. 



Dimensions. — PI. XVIII, fig. 1, measures — 



Greatest anterior posterior diagonal . . 30 mm. 



Length of hinge -line . . . 14 mm. 



Thickness . . . . .11 mm. 



Localities. — England : Roof of the Hard-mine, Ten-foot, Holly Lane, Banbury 

 and Moss seams ; Knowles Ironstone, North Staffordshire ; Grains Ironstone, and 

 Queen's Cross, Dudley, South Staffordshire ; Crawstone, Coalbrookdale, Doe 

 Hill, and Butterley, Derbyshire : Stanley Main, Wakefield. Blue vein, and the 

 Darreupins, Sirrhowy and Cwm Amnion in South Wales. Scotland : The Middle 

 Coal Measures of Shotts, Shelleston, and Kirkwood. 



Observations. — Sowerby's original description of his Modiola earinata is : — 

 "Obliquely elongated; valves boat-shaped, deep; anterior lobe small." This is 

 somewhat vague, but the figure is typical, and it is to be noticed in looking at 

 the list of synomyms that few authors have made use of any other specific name. 



De Ryckholt does not seem to have been aware that anything had been pub- 

 lished on coal-measure Lamellibranchs, and his original specimens seem to have 

 disappeared ; I could find no trace of them either at Brussels or Liege. Mytilus 

 divisus of this author is figured as Mytilus Marise, a footnote in the letterpress 

 pointing out this change. This shell is from the Carboniferous clay of Tournay, and 

 is stated to be " un peu quadrilatere, renflee . . . cote anal elargi, se raccordant 

 par des arcs de cercle obliques avec les cote cardinale et palleale ; ces sont presque 

 droits." This description is very characteristic of Naiadites carinata, and agrees 

 so closely with it that there can be little or no doubt that both shells belong to 

 the same species ; but it is very questionable as to what may have been the shell 

 called by de Ryckholt Mytilus Omaliusianus, which came from coal shale near 

 Vise, and is said to have its " cote buccal coupe obliquement de bas en haut, cote 

 cardinal arque " (the figure shows it to be straight), and the shape of the shell is 

 described as " un pen lanceolee . . . comprimee sur la region palleale, convexe 

 partout ailleurs." 



This species does vary in its shape and convexity, and a series of specimens 

 can- be obtained showing a gradual passage on the one side into N. modiolaris and 

 M. triangularis. Indeed it would be perfectly justifiable to make them all into 

 one species and give them their original names as varieties, seeing that they all 

 seem to occur together, at any rate in the Hard-mine bed of North Staffordshire, 



