Vol. 5, p. 183-185, pi. 7. December 18, 1925. 



Occasional Papers 



OF THE 



Boston Society of Natural History. 



A NEW OYSTER FROM THE CRETACEOUS OF CUBA 



BY PERCY E. RAYMOND. 



An oyster, found during the excavation for a well near the 

 Biological Station and Botanical Gardens of Harvard University 

 (Atkins Foundation) at Soledad, near Cienfuegos, Cuba, proves 

 to belong to a previously unknown species. 



Family OSTREIDAE Lamarck. 



Genus Arctostrea Pervinquiere. 



Arctostrea atkinsi, sp. nov. 



Plate 7, fig. 1, 2. 



Holotype. — No. 15000, Museum of Comparative Zoology. Paratypes, Nos. 

 15001 a, b. 



Description. — Shell large for the genus, extraordinarily thick and massive. 

 No complete valve is known, but large fragments lacking the hinge are lunate, 

 narrow, and taper very gradually to a blunt distal end. The shell is of re- 

 markable thickness, a characteristic apparently attained after almost full 

 length was reached, by the additions of successive lamellae from hinge to tip. 

 Each lamella was of approximately the same length and width as its predecessor, 

 so that the shell remains flat-sided, in spite of the excessive precipitation of 

 calcium carbonate. The outer surface is not preserved, but lamellae which 

 must have been close to the exterior are smooth, and the shell may have been 

 only marginally ribbed. Indications of ribs are seen in the relatively small, 

 toothlike projections along the lateral and terminal margins. The surface 

 may have been similar to that of Arctostrea semiplana (Sowerby) (see Woods, 

 1913, pi. 57, fig. 12a, 13; pi. 58, fig. 1-5) or A. pristiphora (Coquand, 1869, p. 51, 

 pi. 17., fig. 17, 18), in which the greater part of the valve is smooth, but there are 

 short marginal ribs which produce interlocking denticules. 



Only a part of the muscle scar is shown by any specimen. It is small, far 

 back, apparently almost marginal, and not far from the hinge. 



Measurements. — In the absence of any specimen showing the hinge it is not 



Eossible to give the true length and height. These measurements are not, 

 owever, very important in such irregular shells as oysters. The fragment of a 

 right valve used as the holotype has a length of 240 mm. as measured along the 

 curvature of the anterior side, and is 53 mm. in greatest width. The anterior 

 margin makes about half of a circle with a radius of about 90 mm. The crests 

 of the marginal denticulations are about 10 mm. apart, and each is about 5 mm. 

 high. The shell is more than 55 mm. thick near the distal end, and a transverse 

 fracture at the proximal end shows 12 lamellae in a thickness of 10 mm. 



Comparison with other species. — Very diverse opinions exist as 

 to what constitutes a genus or species among the oysters. There 

 seem to be valid reasons, however, for recognizing Pervinquiere's 

 (1911, p. 646) subgenus Arctostrea, and Douville (1911, p. 637- 

 638) has shown that although there are three species of this genus 

 in the Jurassic, it reaches its chief development in the Cretaceous. 

 The best known is Arctostrea carinata (Lamarck), the type of the 

 genus. This species has a wide distribution in Europe and 



