NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 65 



which seems to be very constant. The anterodorsal margin raised and 

 continuing to the close-set umbones; the upper dorsal part forming a 

 lunule with dull periostracum. The shell bluish-white; the periostracum 

 shining yellowish-brown, darkest and most shining in the median part of 

 the shell, which often shows radial striations of darker and lighter color. 

 On the rather prominent keel, the periostracum furnished with dense 

 hairlike protuberances broad at the base, with a dorsal thicker part form- 

 ing the hairs, which have a thinner membrane ventrally; the hairs less 

 numerous toward the dorsal margin. The interior bluish-white; the an- 

 terior margin distinctly bent outward on the dorsal part and continuing 

 slightly behind the umbo, ending in a small "tooth" ; the ligament occupy- 

 ing three fourths of the posterior dorsal margin. The anterior adductor 

 elongate and placed rather high up along the anterior margin ; the pos- 

 terior adductor round, with the continuous retractors starting above the 

 adductor; the anterior retractor fastened in the umbonal cavity. The 

 byssal cavity placed just behind the foot. The dorsal marginal opening 

 small, the branchial part of the mantle margins thickened, the septum 

 with a median flap. 



Holotype: The Allan Hancock Foundation. Length, 88 mm; height, 37.5 

 mm; diameter, 33.5 mm. 

 Type loc: San Diego, California. 



Remarks: This apparently rather common species has been unrecognized 

 for years, though the form is so typical and so different from M. rectus, 

 that they can be separated at a glance. M. neglectus is much more inflated 

 than M. rectus; the ratio of H/L, where L is the total or greatest length, 

 is 35% to 40% in M. neglectus, while in M. rectus the same ratio is 

 25% to 30%. 



Occurrence: M. neglectus seems to prefer deeper water than M. rectus, 

 as the records are from 10 to 57 fms. It lives in sand or mud and spins a 

 "nest" of small particles and fine byssus threads. 



Distribution: Exact distribution unknown, but according to the material 

 at hand it occurs from Monterey Bay, California, to Outer Gorda Bank, 

 Baja California. 



Modiolus sacculifer (Berry) 1953 

 Text-figs. 57 a-b, 58 



Volsella sacculifer Berry, Trans. San Diego Soc. Nat. Hist., vol. 11, no. 



16, 1953, pp. 407-409, PI. 28, figs. 1-2. 

 Holotype: Stanford University, no. 7853. 

 Type loc: San Pedro Harbor, California. 



