PANAMIC-PACIFIC PELECYPODA 385 



Guaymas (Pilsbry and Lowe, type locality); Santa Inez, Gulf of California 

 (Hertlein and Strong). 



Genus STRIGILLA Turton, 1822 



Type species by subsequent designation, Gray, 1847, Tellina carnaria 

 Linne. 



Shell subovate to suborbicular, depressed or convex, usually equivalve, 

 the ends well rounded. Sculptural pattern is characteristic, consisting of 

 evenly spaced, steeply inclined or oblique lines or sulci over the middle of 

 the disk, usually sharply flexed or divaricated along the posterior-umbonal 

 slope (principal line of flexure) forming a line of narrow, sharply acute 

 angles pointing ventrally and often a second line of weaker flexure on the 

 anterior-umbonal slope, sometimes partly effaced by a smooth tract. Sculp- 

 ture over the posterior-umbonal area is simple, formed by unbroken tan- 

 gential sulci or it may also show one or more lines of flexing and sharp 

 zigzag bends. Ligament external, partly immersed in the hinge plate. Hinge 

 with both cardinal and lateral teeth, the cardinal teeth usually small, the 

 laterals stronger; the right valve has strong lateral sockets, the left valve 

 with lateral teeth only. The pallial sinus is deep, its lower limb formed by 

 the pallial line. The prodissoconch of Strigilla is small, smooth, perched on 

 the extreme tip of the beak and followed by the first nepionic stage with 

 fine concentric lines, the sulci beginning later along a weakly defined post- 

 erior keel. Color white, pink or rose-red, uniform or in bands. 



Several names have been given to various Panamic Strigillas by Morch 

 and Philippi but since none of these were figured, their status is somewhat 

 uncertain. Strigilla is said to begin in the Eocene, but the earliest known 

 species which show the characteristic divaricate sculpture are of late Oli- 

 gocene or early Miocene age. Recent species live mostly in shallow water on 

 a sandy bottom. The genus is here divided into the following subgenera: 



L Surface of the shell ornamented with relatively simple, unflexed, incised 

 lines or sulci which cross the disk obliquely but do not show any line 

 of divarication at any point. 



Subgenus Simplistrigilla, new subgenus 



IL Surface ornamentation more elaborate, formed by oblique incised lines 

 or sulci flexed or sharply divaricated by one or more lines of zigzag 

 bends. The principal line of divarication lies along the posterior-um- 

 bonal slope and along it, the points of the acute angles are directed 

 ventrally. The space between this line and the dorsal margin con- 

 stitutes the posterior-dorsal slope or area. 



A, A secondary line of sharp, angular bends extends across the anterior- 

 middle zone; sulci in front of this line are horizontally directed and 

 nearly straight. Distribution: in African and Mediterranean waters. 



Subgenus Aeretica Dall 



B. A secondary line of divarication lies along the anterior-umbonal slope; 

 it is sometimes poorly developed or it may be partly effaced by a 

 smooth tract. 



Ba. Ornamentation of the posterior-dorsal area simple, the sulci fairly 

 straight, tangential to the margin, and if more irregular without a 

 definite pattern. 



Subgenus Strigilla, s.s. 



