1849.] SHARPE ON THE SECONDARY ROCKS OF PORTUGAL. 187 



the valve, and the anterior teeth sloping forwards, which remain 

 visible at all ages of the animal. 



Plate XXIII. fig. 1. Fragment of an old shell, showing the 

 hinge. 



Fig. 2. Hinge of a young shell. 



Mytilus Beirensis, n. s. Pl. XXVI. fig. 1. 



Shell triangular, subfalciform, with a rounded keel curving from 

 ■the beak to the posterior extremity ; covered with numerous concen- 

 tric wrinkles : posterior portion rounded, wdth a few faintly marked, 

 large folds radiating from the beak : anterior side steep, and slightly 

 excavated : beaks pointed and terminal. 



Length 3 inches ; breadth 1^ inch ; thickness 1 inch. 



From limestone of the oolitic series above the coal-beds at Cape 

 Mondego. 



This species is readily distinguished by the waving folds on its 

 posterior slope. The shell is nearly straight when young, and grows 

 falcate gradually. 



Mytilus Morrisii, n. s. Pl. XXII. fig. 5 a & 5 b. 



Shell falciform, with an elevated keel dividing the valves into two 

 very unequal portions, the posterior gibbose and rounded, the ante- 

 rior excavated, and nearly perpendicular to the plane which separates 

 the valves ; with the exception of a small smooth space near the 

 beak on the anterior side, the valves are covered with numerous 

 rounded bifurcating ribs, crossed by concentric lines, which latter are 

 most strongly marked on the anterior side ; the ribs on the posterior 

 side are coarse, and radiate from the beak ; those on the anterior side 

 rise from the keel, and are much finer than the others : beaks pointed 

 and terminal. 



Length 3^ inches ; breadth 1-|- inch ; thickness 1-^- inch. 



Abundant in limestone of the subcretaceous series between Sobral 

 and Torres Vedras. 



I have met with no described species with which to compare this 

 handsome Mytilus. It is named after my friend Mr. John Morris, 

 as a slight acknowledgement of the great assistance which I have 

 received from him in examining the shells described in this memoir. 



Plate XXII. fig. 5 a. Side view. 



Fig. 5 b. Front view. 



OsTRiEA pr^longa, u. s. Pl. XX. fig. 4. 



Flat, elongated, with nearly parallel, fiexuous margins ; attached by 

 nearly the whole lower valve ; hinge-area very long and pointed ; 

 upper valve nearly smooth, with concentric sqaamose lines of growth. 



Length 4 or 5 inches ; breadth 1 or 1^ inch. 



In limestone of the subcretaceous series in the cliifs at the Praia 

 de Ma9ams, north of the Cintra hills. 



This oyster is related to the O. acutirostris of Nilsson, but it ex- 

 ceeds that shell in the length of its narrow hinge-area, which is some- 

 times li inch long, and projects an inch beyond the upper valve. 



