132 UNITED STATES NATIONAL MUSEUM BULLETIN 296 



inner corner of the second segment. The size of this rugose button is 

 greater on the second terminal cirrus, however. 



Despite numerous females, no males were found on Utinomi's 

 material. The larger female from Susami bore one mature male, which 

 I removed intact. Three males were removed from the largest female 

 from Seto. Additional males were observed in the KOH corroded, 

 partial specimens from Seto, and up to four such remains were found 

 on one female, on the exuviae around the horny knob. 



The male is essentially like that of Trypetesa lampas. It occupies a 

 deep pit on the right mantle exterior surface, although it could occupy 

 either or both sides depending on which side were "up." Males are 

 on the shallow side of the female (fig. 35bc). The male attaches by the 

 usual antennules, to the outside mantle surface. The testes extend 

 into a sac descending into the mantle pit, while the penis sheath 

 extends forward toward the aperture. One male (fig. 35f) measures 

 0.90 mm long in toto, although only about 0.76 mm extends beyond 

 the mantle surface. It is approximately 0.12 mm wide at the penis 

 sheath. Bulbous projections at the level of the entrance into the 

 mantle pit are of various widths (see fig. 35d,e). 



In removing the male from the female the antennules broke off. The 

 cellular testicular area could be differentiated from the sperm storage 

 vesicle. The testis is at the deepest portion of the lobe into the mantle 

 pit, and is in close proximity to a black bean-shaped mass assumed 

 to be the naupliar eye. 



Projecting outwardly from the wavy mass of sperm is a penis 

 sheath, although its length and structural detail could not be as- 

 certained. The presence of an actual penis within the sheath of these 

 specimens is doubted. 



Numerous strands of small cells are scattered about Avithin the 

 cuticle of the male, some variously shaded yellowish or opaque. The 

 distal end of the penis sheath bears internal reinforcing fibers, but no 

 external teeth. The exterior of the male is smooth and not ornamented. 



Trypetesa lateralis Tonilinson, 1953, page 374 



Figure 36 



Diagnosis: Trypetesa laterally compressed throughout; no free- 

 swimming nauplius; adult does not exceed 5 millimeters; not bi- 

 laterally symmetrical in mantle structure (operculum on left side of 

 mantle only); male without a penis; male attaches to disk of female 

 or to the cavity wall near the external mantle flap. 



Distribution: In snail shells occupied by hermit crabs, in littoral 

 zone of central California. 



