NO. 1 SOOT-RYEN: THE FAMILY MYTILIDAE 63 



Modiolus rectus (Conrad) 1837 

 Plate 7, figs. 33-35 



Modiola recta Conrad, Jour. Acad. Nat. Sci. Phila., vol. 7, 1837, p. 243, 



PI. 19, fig. 1. 

 Syn.: Mytilus (Modiola) flabellatus Gould 1850. 

 Holotype: Academy of Natural Sciences, Philadelphia. 

 Type loc: Santa Barbara, California, 



Remarks: This slender, elongate species is, in its typical form, easily 

 known from other west coast Modiolus; but it has been confused with 

 M. neglectus, which some authors have supposed to be the form or variety 

 M. flabellatus (Gould). M. rectus is always more elongate and never 

 shows the distinct posterodorsal angle of M. neglectus. The straight dorsal 

 margin extends over to the posterior margin in a long arch without angu- 

 lation. The color of the shell and the periostracum, and the posterodorsal 

 hairs on the periostracum, are very like M. neglectus. The adductors are 

 strong and so are the posterior byssal retractors, while the retractor of the 

 foot and the anterior retractor are relatively weak. The posterior part of 

 the mantle is very thick and shows a broad swollen branchial part. 



Specimens collected by Mr. E. P. Chace at Alamitos Bay, Long Beach, 

 California, May 4, 1954, were heavily infested with a parasite which 

 formed a black, continuous body tapering from the posterior adductor 

 toward the anterior end. This mass could be seen in the sides of the body 

 and had penetrated into the gonads. It consisted of round hyaline ele- 

 ments, 0.1 mm in diameter, with a black central body. The nature of the 

 parasite is not known. 



There has been some discussion about 71/. flabellatus (Gould) 1950, de- 

 scribed from Puget Sound. This form is much larger than the typical 

 rectus, usually with the posteroventral part growing more rapidly than 

 the rest of the shell, so that this part seems to be bent downward. Other 

 specimens are more like the figure of the type in the report of the U. S. 

 Exploring Expedition, reproduced by Oldroyd (1924, PI. 6, fig. 2). 

 These are all large specimens of M. rectus, as is easily seen when the 

 growth lines of the older parts of the valves are studied. Such large speci- 

 mens may be found wherever M. rectus lives and are not confined to a 

 more limited area, though there seems to be some doubt whether small 

 specimens really are found in the northernmost localities. The name M. 

 flabellatus (Gould) is therefore a synonym of M. rectus and not a name 

 for a special or northern form. Large specimens can reach a length of 

 23 cm. 



