380 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



definite smooth edge, keeled, and finely striate; spiral lines of the 

 early portion ornamented by rows of beadlike protuberances, 

 which in later growth may become confluent. 



It has occurred at 10 stations in the Philippine area, as follows: 

 Sulu Sea, off western Mindanao; Sulu Archipelago, near Basilan 

 Island; vicinity of Jolo, Sulu Archipelago; Tawi Tawi Group; off 

 northern Cebu; off eastern Mindoro; and Jolo Sea. 



This species was described by d'Orbignj'^ from ''la mer du Sud a 

 Rawack. " It is very abundant at three adjacent stations — D5132, 

 D5133, D5134, Sulu Sea, off western Mindanao. It is evidently 

 one of the species that Carpenter had from the Philippines, and can 

 be recognized in his description. There is considerable variation 

 in the thickness of the test and the following variety may be dis- 

 tinguished. 



Operculina discoidalis — Material examined. 



OPERCULINA DISCOIDALIS (d'Orbigny), var. INVOLUTA, new variety. 



Description. — Differing from the typical in that the test, instead of 

 being complanate, is more or less involute. The test is usually more 



smooth than the type form. 



This occurs at 12 stations in the area: 

 Balayan Bay and Verde Island Passage; 

 Sulu Sea, off western Mindanao; vicinity 

 of Jolo; Sulu Archipelago; Tawi Tawi 

 Group; Sogod Bay; southern Leyte; 

 Gulf of Davao; China Sea, off southern 

 Luzon; and Sibuko Bay, Borneo. 



There arc a few intermediate forms 

 which seem to show that this involute 

 variety should be placed with 0. dis- 

 coidalis rather than with any of the 



Fig. 16.— Opercui,in.v discoidalis, var. • p xi • o £ 



INVOLUTA, NEW VARIETY. siDE VIEW, othor spccics ol the rcgiou. Some of 

 X 20. From station d5172. the specimens are involute from the 



beginning; others become so after an earh^, more open develop- 

 ment. 



