CARDIOMORPHA LIMOSA. 269 



ligament, which becomes slightly broader and shallower posteriorly, and forms a 

 false escutcheon. Pallial line not exposed. 



Exterior. — The surface is ornamented with fine microscopic concentric lines of 

 growth, parallel to the margins. Shell very thin. 



Dimensions. — PI. XXI, fig. 7, measures — 



Antero-posteriorly . . . .19 mm. 



Dorso-ventrally . . . .14 mm. 



Laterally . . . . .12 mm. 



Localities. — Scotland : Upper Limestone series, excavation for Inland Revenue 

 Buildings at St. George Square and Railway cutting, G-arngad Road, Glasgow ; 

 Thornliebank ; Orchard ; Gare ; Limekilnburn. Middle Ironstone and Coal series, 

 Robroystoue ; Bishopbriggs ; and Calder. Lower Limestone series, Beith ; Craig- 

 englen. 



Observations. — Mr. James Neilson has fortunately unearthed a tablet of shells, 

 in the Museum of Science and Art, Edinburgh, which formed part of the Fleming 

 Collection, bearing a label : " Described in Fleming's British Animals — Corbula 

 limosa." Unfortunately all the figures were drawn before this discovery was 

 made. Fleming did not figure any specimens in his work ; but his description is 

 as follows : " Transversely subtriangular and longitudinally heart-shaped, beaks 

 gibbose, surface slightly striated by layers of growth, shell thin. From shale clay 

 connected with Carboniferous Limestone." It appears that hitherto these shells 

 have been considered as dwarf forms of Oardiomorpha oblonga, with which species 

 they have really nothing in common. The characters distinguishing G. limosa 

 from C. oblonga are the more regularly ovate form, the umbones being not so 

 spirally coiled, the shell never attaining to one-fifth the size of the latter, and the 

 comparatively greater development of the anterior end. 



It is more difficult, however, to distinguish this species from the genus 

 Schizodus, to which it has, from its peculiar shape, a very close resemblance. 

 The hinge and the groove for the external ligament just below the umbo are, 

 however, characteristic of the genus. The dorsal slope is not so hollow, nor is 

 the posterior end so truncate. 



As far as I can ascertain at present this species has not been found in England 

 or Ireland. From the associated fauna — Nucula, Nuculana, and a number of small 

 Gasteropoda — it would appear that the beds in which these species occur were 

 laid down in comparatively shallow water, which probably in a large measure 

 accounts for the small size of the individuals of this species ; for with the excep- 

 tion of G. parva, to be next described, all the representatives of the genus attain 

 a large size. Mr. Neilson says that this species is rare, but moderately common 

 in one bed in the Middle Ironstone and Coal series ; but as this bed is only rarely 

 exposed, during sinking to reach the Lower Fossil Ironstones, few specimens can 



