148 AXEL A. OLSSON 



adductor scar, indistinct and subcentral in position. The beak is generally 

 capped by a small, embryonic shell or prodissoconch with upraised margins, 

 straight or slightly prosogyrous. Hinge line long and straight, aviculoid, 

 the ligament well immersed into the hinge plate, its scar elongated, simple 

 or striated vertically, the ligament itself divided into two parts, the resilium 

 small, dark brown in color and attached to a small, triangular pit near 

 the anterior end, the tensilium longer, of a lighter color, and extending 

 along most of the hinge line behind the beaks. Shell non-nacreous, the 

 surface smooth or marked with weak, radial rays which form short, perio- 

 stracal extensions at the ends. Animal ovoviviparous. 



Some workers place this family near the Limopsidae and Glycymeridae 

 since the soft parts of the animal are said to resemble that of Limopsis. I 

 have followed Bernard in considering the Philobryas as closely related to 

 the Pteriidae, which they resemble in the shape of the shell, hinge line, in 

 being monomyarian and having a short byssus emerging from below the 

 beaks. 



Genus PHILOBRYA Cooper, 1867 

 (Bryophila Carpenter, 1864, not Trietschke, 1825. Lepidoptera.) 

 Type species by monotypy, Bryophila setosa Carpenter. Cape St. 

 Lucas, Lower California. 



Main characters as described for the family, the shell being generally- 

 very small, mytiloid, inequilateral, the anterior side little developed, if 

 any, the posterior side large, high and expanded. Beaks tipped by a relatively 

 large, flat or depressed prodissoconch with thickened, upraised margins, 

 its surface smooth. Surface with a heavy periostracal layer with low, 

 spinously foliated riblets, strongest on the ventral portion. Hinge line 

 straight, its surface and the cardinal area plain and not marked with distinct 

 crenulations. 



Philobrya setosa (Carpenter) Plate 3, figures 12, 12a 



Bryophila setosa Carpenter, 1864, Ann. and Mag. Nat. History, 3d ser., vol. 13, p. 314. — 

 Carpenter, 1872, Smith. Misc. Coll., No. 252, p. 212 (reprint of previous paper). 



Philobrya setosa (Carpenter), 1872, Smith. Misc. Coll. No. 252, p. 21 of Index of Species 

 at end of book.— Dall, 1895, Proc. U. S. Nat. Museum vol. 18, p. 17.— Bernard, 

 1897, Jour, de Conchyl., 3d ser., vol. 45, p. 10, fig. 1, no. 4 and pi. 1, fig 1.— 

 Dall, 1921, Bull. U. S. Nat. Museum, No. 112, p. 17.— Grant and Gale, 1931, 

 Mem. San Diego Nat. Hist., vol. 1, p. 149; Palmer, 1958, Geol. Soc. Amer., Mem. 

 76, p. 67, pi. 1, figs. 11-16. 



This is a small shell, resembling the young of Pinna, Isognonom, and 

 various mytilids but easily distinguished by its large, flattened embryonic 

 shell capping the beaks, and attached to the surface of dead shells by a 

 bundle of small byssal threads emerging between the valves just below the 

 beaks. It is apparently common where found. The margin of the mantle is 

 found dried to the inside of the valve forming a semicircle ring attached 

 loosely to the pallial line. It shows most commonly as a line of alternating 

 light and dark-colered spots, the pale ones ending in short points or teeth 

 while the dark spots have a small eye-spot in front of each. Closed valves 

 are often found filled with newly hatched embryos and their small, white 

 shells can easily be mistaken for those of ostracods; an average embryonic 

 shell measures; greatest length along the straight hinge line 0.34 mm., 

 greatest height 0.2S mm. Beak indistinct but probably placed a little in 



