NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 53 



Remarks: This thin-shelled species, which is very elongate when full- 

 grown, seems to be rather rare. Smaller specimens are very like small 

 Mytella guyanensis, but they can always be separated by the difference 

 in the position of the anterior retractor. 



Mytella speciosa (Reeve) has been labelled Modiola picta Lamarck or 

 Modiola planulata (Lamarck) in many collections. 

 Occurrence: Intertidal, according to Pilsbry and Olsson (1935). 

 Distribution: Northern Peru; Golfo de Fonseca, Nicaragua; Bahia de 

 la Magdalena, Baja California. 



Mytella guyanensis (Lamarck) 1819 



Plate 5, figs. 22-23 ; text-figs. 36, 41-44 



Modiola guyanensis Lamarck, Animaux sans Vertebres, vol. 6, part 1, 



1819, p. 112. 

 Syn.: Mytilus modiolus brasiliensis Chemnitz 1795. 



Modiola semifusca Sowerby 1830, non Lamarck 1819. 



Modiola sinuosa King 1831. 



Modiola f brasiliensis var. mutabilis Carpenter 1856. 

 Holotype: ? 

 Type loc: Guiana. 



Remarks: This widely distributed and variable species cannot, as far as 

 is known, be separated into Atlantic and Pacific races on the basis of shell 

 characters. The samples preserved in the various museum collections 

 studied show the same variations in both oceans. The typical form is a 

 beautiful shell, bright green above the keel and yellow-brown on the 

 ventral and anterior parts, and of a high regular form. Reeve (1857) 

 says that the more uniformly dark-colored form should be considered 

 typical, but the dark-colored forms are very often of a more irregular 

 outline and seem to be the same as Carpenter's var. mutabilis. The green 

 color is often made up of branching green lines on a darker brownish 

 ground color. The anterior adductor is placed high up along the anterior 

 margin, the anterior retractor in the umbonal cavity just behind the 

 umbones ; and a small scar below is very distinct and situated halfway 

 between the adductor and the retractor. In small specimens, the scars of 

 the two parts of the posterior retractors may be separated ; but usually 

 these scars seem to be continuous. The interior of the shell is whitish, 

 distinctly tinged with violet on the muscle scars and on the posterior part. 

 The posterior part of the mantle margin is furnished with branched 

 tentacles very like those of Mytella falcata. 



