MODIOLA PATULA. 59 



edge of the shell. The surface of the shell is divided into two portions by an 

 oblique swelling, which passed downwards and backwards from the umbo to the 

 lower margin near its junction with the posterior border. The lower edge of this 

 swelling is the most marked, and is almost angular in its middle and posterior 

 portions. Below the swelling the shell is compressed and hollowed, so that this 

 part of the surface is placed at a considerable angle with the rest of the shell. 

 The byssal notch was probably at the centre of the lower border, judging from the 

 constriction on the surface of the shell. Above the swelling the shell arches by a 

 gradual curve into the upper and posterior borders, the curve being very rapid in 

 front, and gradually lessening from before backwards, the convexity of the shell 

 diminishing at the same time, but with the smaller convexity the valves become 

 expanded from below upwards. 



The interior is at present unknown. 



The exterior is marked by numerous fine lines of growth, starting from the 

 anterior end, where they are much crowded, but becoming rapidly and widely 

 separated as they pass backwards over the shell, the anterior ones being as much as 

 half an inch apart, but the distance between each line gradually diminishes from 

 before backwards. The interspaces are filled with very fine lines, so that the 

 markings appear to be subimbricate, from the separation of the secondary lines of 

 growth into bundles by the primary. All the bundles and lines of growth have 

 the same contour as the margins of the shell, and when they reach the upper 

 border are rapidly crowded together and terminate in the hinge-line. The shell 

 appears to be very thin. 



Dimensions. — Fig. 2, PL I, measures — 

 Antero-posteriorly 80 mm. 



Dorso-ventrally 40 mm. estimated in incomplete specimen. 



The left valve is 20 mm. deep. 



Localities. — The Carboniferous Limestone of Cork, Millicent. 



Observations. — The original specimen from which M'Coy described this species 

 was probably in the collection of Dr. Haines, of Cork, as the words " communicated 

 by Dr. Haines, of Cork," are appended to the description. At any rate the 

 specimen is not in the Grifiith collection in the Museum of Science and Art, 

 Dublin. The specimen I figure is now in the collection of Mr. Joseph Wright, of 

 Belfast, who informs me that he obtained it from the collection of Dr. Haines. 

 It cannot be the original of M'Coy's figure as is obvious from the most 

 cursory comparison ; it is satisfactory, however, that the specimens now figured 

 come from the same locality as the original. M'Coy points out that " the broad 

 spathulate form and want of posterior angle .... distinguish this from 

 every other Paleozoic species." This is so, at any rate, as far as Carboniferous 

 species are concerned, all the others having a more or less angulated posterior 



