190 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 21, 



shells, and it is possible that farther comparison may show them to 



belong to the same species. 



The external proportions vary materially in different specimens ; 

 in some the length but slightly exceeds the breadth, in others it is 

 fully double the width. 



The dimensions of an average specimen are, length 6 inches ; 

 breadth 4| inches ; thickness 3 inches. 



Plate XXIII. fig. 7. Right yalve of a young sheU. 



Fig. 8. Hinge of the right valve of another specimen. 



Perna polita, n. s. Pl. XXIV. fig. 1 & 2. 



Subrhomboidal; anterior side excavated; front regularly rounded; 

 posteriorly produced into a depressed wing, which is separated from 

 the rest of the valve by a sudden depression : surface covered with 

 very regular scaly lines of growth, between which it is quite smooth. 

 Ligamental hollows broad. 



Length 1^ inch ; breadth 1^ inch ; thickness f of an inch. 



Found in subcretaceous limestones, three miles south-west of 

 Alenquer. 



This is a small neat shell, which wants the usual irregular rough- 

 ness of the Peruse, instead of which it has the general aspect of an 

 Avicula or a Gervilia. In outhne and marking it much resembles 

 Geri'ilia enigma^ D'Orb., except that it entirely wants the anterior 

 wing of that species. 



Tellina Sobralensis, n. s. Pl. XXI. fig. 1 a & 1 5. 



Shell ovato-triangular, gibbose, irregularly striated and wrinkled 

 by concentric lines of growth. Right valve gibbose, with an obscure 

 rounded fold between two broad, shallow depressions : left valve with 

 a broad, shallow depression down the middle, and a rounded, elevated 

 fold near the anterior extremity. 



Length 2\ inches ; breadth 2>\ inches ; thickness \\ inch. 



From subcretaceous beds between Sobral and Torres Yedras. 



Neither the hinge nor the interior of this shell have been seen. 



Plate XXI. fig. \a k,h. Two views of the same specimen. 



Trigonia Lusitanica, n. s. Pl. XXII. fig. 4 « & 4 5. 

 Lyrodon liter atum ?, Goldf. pl. 136. f. 5 c, & 5 d, excluding f. 5 a, h, 



Ovato-subtriangular ; anterior side short and nearly straight ; pos- 

 teriorly elongated ; front regularly curved : ornamented with curved 

 rows of tubercles which bifurcate towards the anterior angle of the 

 shell, and which are continued over the anterior side in irregular, 

 faint, sharp ridges. Tubercles of two sizes, which might be separated 

 by a diagonal line dra^vn from the umbo to near the middle of the front 

 of the shell. Posterior side of the valve sloping, dirided into two 

 uneven parts by a deep furrow : the hinder area crossed by rows of 

 small tubercles, the front area coarsely striated. Surface of the shell 



