68 AXEL A. OLSSON 



Generally less than 15 mm. in length, compressed, of a dark chestnut- 

 brown color, its shape and sculpture like that of a small crassatellid, the 

 posterior side much longer than the anterior, narrowly attenuated and 

 squarely truncated at the end. 



This is a common species off the coast of California, often dredged 

 in waters of 20 to 200 fathoms. Hertlein and Strong record the species 

 off the Mexican coast (east of Cedros Island). Dall (1921) gave its range 

 as from Puget Sound to Panama, but the species is probably not a member 

 of the Panamic-Pacific fauna. 



Genus ADKAIfA H. and A. Adams, 1858 



Type species by subsequent designation, Stoliczka, 1871, Nucula 

 (Adrana) lanceolata Lamarck. No locality cited. (See Hertlein and Strong, 

 1840, p. 406). 



Shell elongate or narrowly lanceolate, compressed, the dorsal margin 

 nearly straight with small, subcentral beaks, the ventral margin rounded 

 and often sinuate near the ends. No rostral area but a narrow, flattened 

 lunule and escutcheon is usually well developed, bounded by a rounded, 

 often crenate umbonal ridge. Ligament internal and attached to a wide, 

 often weakly bilobed chondrophore placed under the beak and directed 

 anteriorly. Hinge teeth numerous and arranged in an anterior and posterior 

 series. Pallial sinus rounded and of moderate size. Sculpture smooth or 

 composed of threadlike, concentric ridges, sometimes becoming oblique 

 posteriorly. 



Drift valves of these lovely shells are often common on some sandy 

 beaches. About six valid species are recognized in this review and as shown 

 in the keys belong to two well-marked groups. 



Key to species of Adrana 



L The dorsal margin is nearly straight, the lower or ventral margin is 

 commonly sinuated towards the anterior end. 



A. Shell relatively narrow and slender, the ratio of height to length about 

 1 to 5. 



1 _ ...„ ^ A. sowerhyana 



B. Shell higher, ratio of height to length about 1 to 4 or less. 



2. Length about 38 mm, the beaks placed near the anterior one-third. 

 Gulf of California. PI. 3, fig. 7. 



A. penascoensis 



3. Average length about 60 mm. The beak is placed a little anterior of 

 the middle. 



A. ctdtrata 



4. Shell larger, often exceeding 100 mm. in length. Beaks placed quite 

 close to the middle. 



A. suprema 

 n. Dorsal margin arched at the beak, concave behind. 



C. Concentric sculpture developed over the whole surface of shell. 



5. Shell length about 35 mm. The lines of sculpture are relatively fine 

 and developed uniformly over the whole disk. 



A. crenijera 



6. Shell smaller, the lines of sculpture heavy and coarse on the anterior 

 side. 



A tonosiana 



