36 MOLLUSCA FROM THE GREAT OOLITE. 



gryphoid, the right valve somewhat concave ; the valves ornamented with irregular varices, 

 sometimes dichotomous, and imperfectly radiating. The smaller valve has a few unequal 

 nodules upon the varices. Apices of the valves oblique and attenuated. 



The thickness of the larger valve is moderate, the smaller valve is rather thin ; 

 specimens vary much in the convexity of the larger valve and in the varices, the latter 

 being sometimes not distinguishable; the apices are much produced, attenuated, and 

 curved forwards, more especially that of the larger valve. The almost constant manner in 

 which the larger valve is loaded with adherent shells is a considerable obstacle to the 

 determination of species, this, together w T ith some variation in the figure of the valves, 

 suggests doubts which are only to be removed by a comparison of numerous specimens. 



Height, 5^ inches ; opposite diameter, 4J inches ; diameter tlirough both the valves, 

 2| inches. 



Localities. Minchinhampton Common, where it is not unfrequent; Scar Hill, near 

 Nailsworth, in the freestone of the Inferior Oolite, where it occurs very rarely. 



In the Great Oolite of Comb Down, near Bath. (Museum of Practical Geology, pre- 

 sented by Mr. S. P. Pratt.) 



Mytilus, Linn., 1758. 



Mytilus et Modiola, Auct. 



Gen. Char. Shell longitudinal, oblique ; umbones terminal or subterminal. Hinge 

 lateral, linear, and without teeth, ligament marginal and somewhat internal, muscular 

 impression elongated, club shaped, and placed somewhat laterally; anterior impression 

 very small. 



Mytilus Sowerbyanus, D 'Orb. Tab. IV, fig. 1. 



Mytilus Sowerbyanus, D'Orb. Prod. Pal. i, p. 282, 1850. 

 Modiola Sowerbyana, Bromi. Leth. Geog., p. 233, t. 15, f. 13, 1851. 



— plicata, Sow. Min. Con., t. 248, f. 1, 1819. 



— — Zeiten. Petref., t. 59, f. 7, 1835. 

 Mytilus plicatus, Gold/. Petref., p. 175, t. 130, f. 12, 1840. 



Testa elongatd, soleniformi, antice angustd, obtusd, poslice dilatatd, angulo obliquo 

 tenui bipartitd, parte inferiore et anticd Icevigatd, superiore et posticd arcuatim plicatd. 



Shell elongated, pod-shaped, anterior part narrow and obtuse, posterior ddated, divided 

 into two portions by a thin oblique angle, inferior and anterior part smooth, superior and 

 posterior part with numerous curved folds. 



The hinge margin is very much elongated and slightly curved, the inferior border is 

 slightly concave and acute. The short costae upon the superior border are parallel, oblique, 

 and are impressed with numerous densely-arranged curved lines, which upon the lower 

 portion of the shell are parallel with the inferior border. 



