46 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Brachidontes playasensis (Pilsbry and Olsson) 1935 

 PI. 3, fig. 16 



Modiolus (Brachydontes) playasensis Pilsbry and Olsson, Nautilus, vol. 



49, 1935, p. 17, PI. 1, fig. 4. 

 Holotype: Academy of Natural Sciences of Philadelphia. No. 164617. 

 Type loc: Playas, Santa Elena, Ecuador. 



Remarks: This species is characterized by the fine radial sculpture of 

 nearly the same strength over the whole surface and by the light brown 

 color arranged on a white shell, partly concentric and partly in irregular 

 blotches. The radial striae seem not to bifurcate except along the extreme 

 dorsal and posterior margins, but the striae grow broader from the nearly 

 smooth oldest part of the shell. There are fine, close-set concentric lines 

 which cross the ribs and interspaces. The margins are finely crenulated 

 except on the anterior part of the ventral margins. There are three teeth 

 diverging from the umbones ; the anterior margin is bent outward prox- 

 imally and crenulated. The muscle scars are indistinct, the anterior ad- 

 ductor seems to be placed along the anterior border, which protrudes 

 slightly beyond the umbones. 



There might be some doubt if the specimen here referred to B. playa- 

 sensis really is this species. The figure of the type of playasensis shows a 

 shell very like Brachidontes puntarenensis in outline but apparently with 

 a finer sculpture. The main difference between these two species seems 

 to be that the sculpture is obsolete anteriorly in one but distinct in the 

 other. 



Occurrence: No data available. 

 Distribution: Ecuador. 



Brachidontes puntarenensis (Pilsbry and Lowe) 1932 

 Plate 3, fig. 14; text-fig. 29 



Mytilus (Hormomya) puntarenensis Pilsbry and Lowe, Proc. Acad. 



Nat. Sci. Phila., vol. 84, 1932, p. 104, PI. 10, fig. 6. 

 Holotype: Academy of Natural Sciences of Philadelphia. No. 155629. 

 Type loc: Puntarenas, Costa Rica. 



Remarks: Through the kindness of Mr. E. P. Chace, a sample of the 

 paratypes from the San Diego Museum was studied. Though the authors 

 described it as a Hormomya and compared it to Mytilus exustus, this 

 species belongs to the genus Brachidontes. The anterior margin is nar- 

 row, but the angulation in the hinge is observable, the muscle scars and 

 the radial sculpture agree with Brachidontes as here interpreted. There 

 might be a possibility that Dunker used the name Mytilus adamsianus 



