NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 51 



Modiola mutabilis auct. non Carpenter 1856. 

 Mytilus nitens auct. non Carpenter 1856. 

 Modiolus arciformis Dall 1909. 

 H oh type: ? 

 Type loc: Rio de Janeiro. 



Remarks: This extremely variable and widely distributed species is found 

 under many different names in museum collections. There is some doubt 

 about the oldest name for the species. If Mytilus strigatus Hanley, PI. 24, 

 fig. 34, with the description on p. 251 as of Hinds 1844, really represents 

 the species, the name has to be changed accordingly. The original diagnosis 

 does not mention any locality. On p. 388, Hanley says that Hinds in- 

 tended to describe this species but never did it, and it has subsequently 

 been termed Mytilus falcatus by Orbigny (S. Am.). 



Reeve (1857) concurs with Hanley in giving the Philippine Islands as 

 the habitat for Modiola strigata Hanley, and considers that Mytilus 

 strigatus Hanley is the same species. Reeve's species is thought to be 

 Mytilus sinuatus Reeve by Lamy (1936), who uses Mytilus strigatus 

 Hanley for the Mexican species. There seems, however, to be no justifi- 

 cation for this ; so if the locality, Philippine Islands, is correct, it is safest 

 until otherwise proved, to use Mytella falcata (Orbigny) for this species. 

 Orbigny (1846) used the name Mytilus falcatus in the description, 

 p. 645, but the name Mytilus charruanus for the figure, PI. 84, figs. 

 38-39. 



Carpenter (1856) described Modiola nitens as from California but 

 later (1864) said: "The shell was erroneously described as from 'Cali- 

 fornia' in P. Z. S., and does not appear in the Reigen Mazatlan Cat. : ^ 

 M. suhpurpureus, Mus. Cum." Dall (1909) described Modiolus arci- 

 formis on two fragments from Ecuador. Though these fragments repre- 

 sent rather arcuate specimens, they are conspecific with ordinary Mytella 

 falcata and the same form is also found on the Atlanic side. 



Mytella falcata has nearly terminal umbones and a short rounded 

 anterior margin, sometimes narrow, sometimes broader. The lunule is 

 furnished with radiating folds forming three or four teeth on the anterior 

 margin. Usually there is a distinct dorsal angle, but sometimes the dorsal 

 margin is evenly curved. Specimens from different localities may often 

 appear to belong to different species. The same forms, however, are re- 

 corded from both oceans and from widely separated localities. The color 

 usually is distinct, with yellowish-brown anteroventral part and green 

 dorsal part. The green color may be uniform or shown as dark criss-cross 

 bands on a lighter surface. Some populations are nearly black, but a 



