1849.] SHARPE ON THE SECONDARY ROCKS OF PORTUGAL. 185 



to Lisbon, furnislies in abundance the following varieties of M. D'Or- 

 bigny, O. Boussingaultii, O. flabellata, 0. Matheroniana, of which 

 the first is the most abundant form. 



The limestone beds of the coast north of Cintra at the Praia de 

 Ma9ams, which lie low in the subcretaceous series, are crowded with 

 the same three varieties, O. Boussingaultii, D'Orb., O. jlahellata, 

 D'Orb., O, Matheroniana, D'Orb., so that in Portugal the different 

 varieties of this species are found together in the same bed both in 

 the upper and the lower part of the cretaceous series. 



The serrations which run partially round the interior of the valves 

 at a slight distance from their edge (D'Orb. pi. 468. f. 5, pi. 485. 

 f, 7 ; Goldf. pi. 87. f. oc), depend on the age of the shell, and must 

 not be taken for specific characters : they are seldom seen on very 

 young shells, and become obliterated and covered up in very old ones. 

 The tooth which M. D'Orbigny assigns as one of the characters of 

 the O. Mather oniana, p. 738, and pi. 485. f. 7, is also an uncertain 

 character, varying in development in individuals from the same lo- 

 cality and often obliterated in old shells. 



As the principal diiferences between the three forms, O. Boussin- 

 ffaidtii, Jlabellata and Matheroniana, appear to consist, according to 

 M. D'Orbigny, in their having been found in France in different beds, 

 it may be hoped that now they have been found together in Portugal, 

 they may be admitted to be one species. 



In the subcretaceous beds north of Cintra this species is found from 

 1 to near 5 inches in length ; the plications are faint in those parts 

 of the shell which are of later growth, and towards the edges the old 

 shells are nearly smooth ; at this stage of growth the shell somewhat 

 approaches the form of the E. sinuata. 



ExoGYRA Olisiponensis, u. s. Pl. XIX. fig. 1 & 2. 



Shell nearly hemispherical : upper valve thick, slightly gibbose, 

 covered with regularly concentric scales, the beak incurved in the 

 plane of the valve : lower valve very thick and very gibbose, regu- 

 larly rounded on the anterior margin and somewhat produced poste- 

 riorly : the surface squamose, with the edges of the scales raised up 

 into short ribs, of which there are ten or twelve near the margin of an 

 old shell ; in some specimens the ribs are nearly continuous, in others 

 they only occur near the margin of the scales, while in others they 

 are hardly visible ; the surface of the valve between the ribs is nearly 

 smooth : beak of the lower valve laterally involute ; the surface of 

 attachment usually small. 



In the upper beds of the hippurite limestone at Lisbon. 



Length 4 inches ; breadth 3 inches ; thickness 2^- inches. 



In the young state, when about 1^ inch long, this shell resembles 

 E. laciniata, Nilsson, but the great size which it reaches and the 

 greater convexity of its lower valve have prevented me from uniting 

 them. 



Plate XIX. fig. 1. Lower valve, strongly ribbed. 



Fig. 2. Upper valve of a smaller specimen. 



