NAIADITES CARINATA. 139 
Interior.—The arrangement of muscle-scars, and the hinge-line, differ in no way 
from the descriptions given under Naiadites 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.—P|. XVIII, fig. 1, measures— 
Greatest anterior posterior diagonal : . 30mm. 
Length of hinge-line_ . : . 14mm. 
Thickness . delim: 
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 
Darrenpins, Sirrhowy and Cwm Ammon in South Wales. Scotland: The Middle 
Coal Measures of Shotts, Shelleston, and Kirkwood. 
Observations.—Sowerby’s original description of his Modiola carinata 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 Liége. Mytilus 
divisus of this author is figured as Mytilus Mariz, 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 quadrilatére, renflée . . . cdté anal élargi, se raccordant 
par des arcs de cercle obliques avec les cété cardinale et palléale ; ces sont presque 
droits.’’ This description is very characteristic of Naiadites cariata, 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 
Visé, and is said to have its ‘* c6té buccal coupé obliquement de bas en haut, cdté 
cardinal arqué” (the figure shows it to be straight), and the shape of the shell is 
described as ‘“‘un peu lancéolée . . . comprimée sur la region palléale, 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, 
