124 AXEL A. OLSSON 



Volsella (Volsella) guyanensis (Lamarck), Hertlein and Strong 1946, Zoologica, vol. 



31, pt. 2, pp. 72, 73. 

 Mytella guyanensis (Lamarck), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, 



vol. 20, No. 1, pp. 53-55, pi. 5, figs. 22, 23; text-figs. 36, 41-44, 



The shell is oblong, obliquely wedge-shaped, relatively thin, the hinge 

 margin is straight, more than half the total length, the basal margin 

 descends straight or is deeply impressed. The sculpture is produced by 

 well-developed, raised, regular concentrics along the posterior slope and 

 finer, smoother growth lines on the ventral side. The periostracum is thin, 

 its coloration divided into two contrasting zones; on the posterior portion, 

 the color is a dull or satiny greenish black, generally with a fine pattern of 

 zigzagged or divaricating lines of green showing through; on the ventral 

 slope the color is typically a glossy brown. There is often a ray of brown 

 along the lower side of the umbonal slope which because of its dull luster 

 contrasts sharply with the polished brown surface behind it. The umbones 

 are usually eroded. 



Length 70 mm.; height 44 mm.; diameter 32.8 mm. 



Guayaquil, Ecuador, market. 



Shells from Ecuador and northern Peru have the ventral side flattened 

 or deeply impressed and the umbones are so badly eroded as to expose the 

 pearly inner layer over a wide area; the habitat of this mussel is along the 

 mud flats in front of mangrove swamps or in the adjacent estuaries and 

 esteros. In Ecuador, this mussel is highly esteemed as food and appears 

 in the markets and is served regularly in hotels and restaurants. 



Range — Lower California to northern Peru; also along the Caribbean 

 coasts of Venezuela southward to Brazil. Panama: Pearl Islands; Garachine. 

 Canal Zone: Venado Beach. Ecuador: Esmeraldas; Cojimenes; Guayaquil. 

 Peru: Tumbez. 



Mytella speciosa (Reeve) Plate 14, figure 6 



Modiola speciosa Dunker in Reeve, 1857, Conch. Icon., vol. 10, Modiola, pi. 7, fig. 35 



Tumbez. 

 Modiolus speciosus (Dunker), Maxwell Smith, 1944, Panamic Marine Shells, p. 53, 



fig. 698. 

 Volsella (Amygdalum) speciosa (Dunker), Hertlein and Strong, 1946, Zoologica, vol. 



31, pt. 2, p. 73. 



Shell elongate and slender, very thin, smooth, the dorsal and ventral 

 margins straight, not quite parallel but diverging at an angle of about 

 9 degrees. Beaks very small, not quite terminal, the widely rounded anterior 

 end extending beyond them shortly. Posterior margin oblique, sloping down- 

 ward, its dorsal junction widely rounded, more narrowly rounded or atten- 

 uate at the ventral end. Periostracum is very thin, overlying a dull-white 

 surface. The posterior slope is generally colored in various shades of green 

 or green-brown, often concentrically banded or minutely flecked with brown, 

 the long, ventral slope is brown. Interior nacreous, iridescent. 



Remarkable for its slender, thin shell and beautiful coloration. Generally 

 rare. Very young shells (length 36 mm.) have the same shape as the 

 adult. Large specimens may attain a length of over 100 mm. 



Range — Lower California to northern Peru. Mexico: Magdalena Bay, 



