140 AXEL A. OLSSON 



small holes or pits in rock walls. These clams have the shape of a small 

 Mytilus, with pointed, terminal beaks, a small septum in the beak like 

 Septifer and a smooth or concentrically wrinkled surface covered by a dark- 

 colored periostracum. They are gathered by the Cayapas Indians of Ecua- 

 dor for food. Mytilopsis adamsi Morrison® was described from a lagoon 

 at the mouth of Musselshell Creek on San Jose Island, Pearl Islands, Pan- 

 ama. The same species may also occur on the mainland. 



Shell mytiloid, the anterior adductor attached to a shelflike platform 

 or thickened septum in the apical section, sometimes with a small, tooth- 

 like lamina or apopthysis below the septum for the attachment of the byssal 

 muscle. Habitat, fresh- or brackish-water. 



Genus MYTILOPSIS Conrad, 1857 



{Praxis H. and A. Adams, Dec. 1857) 



Type species by monotypy, M. leucophaeatus Conrad, 1831. Recent, 

 southeastern coast of the United States. 



Shell mytiloid, non-nacreous, with sharply pointed beaks at the extreme 

 anterior end. Hinge line with a furrow for the attachment of the ligament 

 along and within the dorsal margin for most of its length. Adductors two, 

 the posterior one elongate or club-shape, the anterior seated on a flat shelf 

 or septum in the beak roofing over the umbonal cavity which extends well 

 under it. There is a small lamina under the septum for the support of the 

 byssal muscle. Externally the shell is covered with a coarse periostracum, 

 the surface below, smooth or concentrically striated. 



Mytilopsis trautwineana (Tryon) Plate 84, figure 8 



Septifer Trauiivineana Tryon, 1866, Am«r. Jour. Conch., vol. 2, p. 302, pi. 20, fig. 8 

 Rio San Juan (lat. 4° North) ; New Granada (Colombia). 



Praxis Milleri Clessin, Miller, 1879, Malak. Blatter, tonne 26, pp. 179, 180, tav. 15, fig. 

 7 Rio Verde, Esmeraldas, Ecuador. 



Praxis Ecuadoriana Clessin, Miller, 1879, op. cit., pp. 180, 181, tav. 15, fig. 8 Rio 

 Cayapas, Esmeraldas, Ecuador. 



Shell narrowly or broadly mytiliform with the general axis inclined 

 about 45 degrees with the hinge line placed horizontally. Hinge line a little 

 shorter than the length of the shell, its posterior margin straight or rounded 

 towards the end, the anterior side weakly impressed so that the umbonal 

 slope appears arched or crudely angular. Internal septum in the beak rather 

 large, excavated, the byssal muscle scar showing plainly on the end of the 

 apophysis below. Periostracum dark-brown to nearly black in color, coarsely, 

 concentrically wrinkled. Interior glossy, bluish-white in color, blotched or 

 streaked with white or black. 



Length 16 mm.; height 24.4 mm.; diameter 9.6 mm. 



Rio Cayapas, Esmeraldas, Ecuador. 



This is a fresh-water species. It was observed on several occasions by 

 the author living in parts of the Rio Cayapas River system in Ecuador, and 



•Morrison, J. P. E., 1946, Smith. Misc. Coll., vol. 106, No. 6, pp. 46, 47, pi. 1, figs. 



