434 CARBONIFEKOUS LAMELLIBRANCHIATA. 



as it approaches the lower margin. The posterior third of the valve is more 

 regularly convex, there being only a very slight amount of flattening along the 

 dorsal slope. 



Interior. — The adductor muscle-scars are obscure. Pallial line not observed. 

 Hinge-plate thickened, leaving a broad groove in casts. 



Exterior. — The surface is covered with irregular concentric folds and wrinkles, 

 made up of bundles of strise and lines of growth ; the whole crossed by numerous 

 low tubercles arranged in radiating rows, often only visible under the microscope. 

 They occur even in the hollow of the escutcheon ; but in the anterior portion of 

 the shell the tubercles may become confluent. Shell thin. 



Dimensions. — As all the full-grown examples I have are imperfect, I give the 

 dimensions of a very young example, PI. XLIX, fig. 5. 



Antero-posteriorly . . . .31 mm. 



Dorso-ventrally . . . . 18 mm. 



From side to side . . . .15 mm. 



PI. XLIX, fig. 7, a large valve, measures— 



Antero-posteriorly (estimated) . . .64 mm. 



Dorso-ventrally . . . .80 mm. 



Localities. — England : the Carboniferous Limestone of Park Hill, Thorpe Cloud, 

 and Castleton, Derbyshire ; Hill Bolton, Yorkshire ; and the Poolvash Limestone, 

 Isle of Man. Scotland : the Upper Limestone series at Garngad Road, Glasgow, 

 and Thornton; the Lower Limestone series of Hind og glen, Dairy, and Auchens- 

 keith, Ayrshire. 



Ohservations. — The genus Tellinomorpha was founded by de Koninck to receive 

 a single valve of this species (see page 431), which occurred in the Upper 

 Carboniferous Limestone of Belgium. I have been fortunate enough to collect 

 many specimens from the British localities mentioned above, several of which 

 have the very beautifully marked characteristic test preserved ; but few of the 

 specimens are complete, and casts of the interior, which I have yet obtained, 

 unfortunately exhibit no details of the muscle-scars, pallial line, or hinge. Mr. 

 Smith has obtained two very perfect examples from Scotland. De Koninck did 

 not recognise the peculiar character of the surface, but was able to describe and 

 figure the hinge-plate. With his original description I am not able entirely to 

 agree ; for his specimen being very deficient at the posterior end, the shape is 

 hardly cuneiform ; nor, if he had noticed the actual contour of the earlier lines of 

 growth, could he have said that the posterior end was truncate, or, looking at the 

 figure, that the hinge-line was straight. 



A comparison of de Koniuck's type specimen, preserved in the Musee Royal 

 d'Histoire Naturelle, at Brussels, and the figure shows that the dotted contour 

 for the posterior and lower part of the valve is very incorrect ; for, if the true 



