188 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



OsTR^A PUSTOLOSA, 11. s. Pl. XXIV. fig. 4a & 4b. 



Very thick, irregular, ovate, transverse or rhomboidal, deep ; hinge- 

 area very large. Lower valve gibbose, slightly attached, the rest of 

 the valve irregularly covered with warty swellings : upper valve flat, 

 nearly smooth or slightly pustulose. 



Length 2^ to 3 inches ; breadth about 2 inches. 



Very abundant in limestones of the subcretaceous period between 

 Torres Vedras and Sobral. 



This oyster appears to have increased its depth and thickness, 

 while adding very little to its circumference. It is frequently broader 

 than long ; and the large hinge-area often covers more than a third 

 of the area of the shell. These characters and the warty or pustu- 

 lose appearance of the surface distinguish it readily. 



Plate XXIV. fig. 4 a. Lower valve. 



Fig. 4 b. Hinge of lower valve. 



Pecten (Janira) inconstans, n. s. Pl. XIX. fig. 3a & 3b. 



Shell heptagonal, nearly circular ; convex below, slightly concave 

 above. The lower valve nearly hemispherical, with an incurved 

 umbo, ornamented with about twenty elevated, rounded, nearly equal 

 ribs, separated by unequal rounded hollows, in some of which there 

 are one or two fine ribs. Every fourth rib is longer than the rest, 

 and is produced into the angles of the shell ; some of these longer 

 ribs are also more elevated than the rest. 



Upper valve shghtly convex, covered with seventy to eighty ribs of 

 varying form and size, separated by very unequal hollows. The 

 principal ribs which run to the three front angles of the shell are 

 divided into four by one broad central furrow, and two slight lateral 

 furrows down each, and they are very unequally elevated, one being 

 always much more prominent than its fellows : towards the lateral 

 angles the ribs are much subdivided and very unequal. 



Both valves are covered by well-marked concentric lines. 



Ears small, placed very forward on the upper side of the shell. 



Diameter 3 to 4 inches. 



In the upper beds of the hippurite limestone at Lisbon j not 

 common. 



This is closely related to Pecten quadricostatus, and, as in that 

 shell, every fourth rib on the lower valve is of more importance than 

 its fellows ; but on. the upper valve the ribs are more angular, and 

 more numerously and irregularly divided than in that species. The 

 most singular feature in the shell is the irregular elevation of the 

 principal ribs, one of the two middle ones being always depressed 

 and the other elevated, which gives a very awkward appearance to 

 the shell : all the specimens seen agree in this respect. The ears are 

 broken in all my specimens. 



If all M. D'Orbigny's species of Janira are considered distinct, 

 this must also rank as a distinct species ; but if farther observation 

 leads us to throw many of those together, then this shell will pro- 

 bably be regarded as only a variety of P. quadricostatus. 



