26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



define shallow and narrow umbonal chambers. Muscle field short and 

 narrow, the diductors surrounding the large adductors and with small 

 adjusters in a posterolateral position. Pallial marks strongly im- 

 pressed, the vascula media extending from the anterolateral end of 

 the muscle field to converge anteriorly on the long tongue. Lateral 

 branches few. 



Brachial valve interior with deep corrugated sockets bounded by 

 strong socket ridges ; crura of falcifer type, moderately long crescentic 

 in section, scimitarlike and attached to the socket ridges by prominent 

 outer hinge plates. Inner hinge plates absent. Vascula media widely 

 divergent. 



Type species (by original designation). — Hemithyris beecheri Dall, 

 Proc. U. S. Nat. Mus., vol. 17, p. 717, pi. 31, figs. 1-4, 1895. 



Comparison. — Basiliola is characterized by its smooth shell, elabo- 

 rate pedicle collar, conjunct and auriculate deltidial plates, small round 

 to longitudinally elliptical foramen and the broad outer hinge plates 

 of the cardinalia. Basiliola differs from Rhytirhynchia, which it other- 

 wise resembles, in lack of anterior costation. It differs from Aetheia 

 in the nature of the foramen and the lack of inner hinge plates in the 

 cardinalia. Aphelcsia is similar externally to Basiliola and has a similar 

 foramen but its cardinalia are quite distinct in lacking outer hinge 

 plates. Basiliola differs from Probolarina by its smooth exterior. 



Geological horizon. — Basiliola is known from Pliocene to Recent. 



Distribution. — The known Pliocene species of Basiliola are from 

 Okinawa. Yabe and Hatai (1935) identified one Okinawa form as 

 Neohemithyris lucida and identified its age as Pleistocene. Cooper 

 (1957) described specimens of this species from the same place as 

 new, and another, not named, in addition. Furthermore, the U. S. 

 Geological Survey now dates the beds producing these specimens as 

 late Pliocene. So far as known these are the only fossil basiliolas 

 known. 



Basiliola occurs in modern seas around the Hawaiian Islands, Japan, 

 Fiji, Borneo, Malay Archipelago, the Celebes, and Philippine Islands. 



Bathymetric range. — Each of the species assigned here to Basiliola 

 has a different bathymetric range and different temperature tolerance. 

 Basiliola beecheri ranges in depth from 143 fathoms down to 313 

 fathoms, and the temperature range is 43.8 F. to 60.8 F. Basiliola 

 pompholyx usually occupies deeper water, from about 150 fathoms 

 (275 meters, Jackson and Stiasny, 1937, p. 10) down to 1,105 fathoms, 

 and with a temperature tolerance between 43. 3 ° F. and 52 ° F. Ba- 

 siliola elongata occurs in 24 fathoms but the temperature is not known. 



