120 AXEL A. OLSSON 



SO. In fresh shells, the periostracum is thin, vernicose and dark olive- 

 brown to nearly black in color with some lighter streaks showing through. 

 Beneath the periostracum, the color of the shell is variable, in some speci- 

 mens, it is white or grayish white; others are grayish purple flecked 

 and rayed with lighter patches. Sculpture consists of numerous, small, 

 radial riblets, developed uniformly over the surface except in the middle 

 ventral zone which is smoothish. Inner margin of the valves crenulated 

 all around except for a small space along the ventral side which is smooth; 

 the ligamental margin is always strongly crenulated. Extreme anterior or 

 lunular side has a few, small, strong riblets forming crenulations at the 

 margin. Impression of the adductor and retractor muscles as described for 

 the genus. 



Length 14.1 mm.; height 9.6 mm.; diameter 5.6 mm. Esmeraldas, 

 Ecuador. Holotype ANSP 218929. 



Length 17 mm.; height 11 mm.; diameter 7.4 mm. Esmeraldas, 

 Ecuador. Paratype ANSP 218930. 



Range — Ecuador. Ecuador: Esmeraldas. 



ScoUmytilns (Scolimytilns) aeqnatorlalis, new species Plate 12, figures 9-9b 



The shell is small (length about 10 mm.), obliquely elongated, with 

 anterior, almost terminal beaks. The posterior-umbonal axis is slightly 

 curved, convex and high along the middle zone; the ventral side is flattened 

 or moderately impressed, the shape of the shell therefore somewhat arcuate. 

 Hinge line straight and about half the length of the shell, the ligament 

 nearly as long; beyond the end of the ligament or its scar, the posterior 

 margin turns downward at an angle of 150 degrees, continues straight 

 for a distance and then curves evenly forming a rounded end, or it may 

 bend more sharply so that the end of the shell appears truncated. The 

 periostracum is thin, vernicose, and imparts to the surface a glossy, 

 varnished appearance. External color of the shell is two-toned, dark purplish- 

 brown to nearly black on the dorsal side of the umbonal ridge and a lighter 

 olive-yellow on the ventral side, these two zones of color showing through 

 into the interior. Beneath the periostracum, the sculpture is plain or 

 smooth except for some weak riblets generally present on the posterior- 

 dorsal surface. The inner margins of the valve is smooth except for crenu- 

 lations present above the ligament. Hinge teeth small, confined to the space 

 below the beaks supplemented by weak crenulations along the short, an- 

 terior margin. Posterior adductor scar of medium size, pioe-shaped. 



Length 10.1 mm.; height 6.8 mm.; diameter 6 mm. Punta Centinella, 

 Santa Elena Peninsula, Ecuador. 



Holotype, ANSP 21927; paratype, ANSP 21928. 



Range — Coast of Ecuador and northwestern Peru. Ecuador: Punta 

 Centinella, Santa Elena, on rocks at medium tide level. Peru: Paita. 



Subgenus AEIDIMTTILUS, new subgenus 



Type species Mytilus adamsiana Dunker. 



Shell small, mytiliform with ribbed sculpture, usually divided, the ribs 

 on the posterior-dorsal side of the umbonal ridge much coarser. Ventral 

 side usually strongly impressed resulting in a high, angular umbonal ridge 

 and often a distorted appearance to the whole shell. Adductor and pallial 

 impressions united, but smaller and narrower than in Scolimytilns . 



