OPISTHOBRANCHIATE MOLLUSC A FROM MONTEREY BAY. 145 . 



Labial disk oval, convex, about 0.9 mm. in diameter; its cuticle thin and colorless. The light 

 yellow armature (pi. x.x, fig. 74) a pavement of minute hooks (pi. xx, iic;. 79) confined mainly to a 

 triangular area on the lower and lateral borders of the opening. The lowermost portion of the labial 

 armature is free from hooks and is occupied by a broad, slightly concave thickening of the cuticle, 

 narrowing to a point posteriorly and anteriorly forked, divergent into two bladelike proce.sses which 

 project freely a short distance from the margin (pi. xx, tigs. 75, 76), the whole structure being shaped 

 much like an arrowhead, the point directed backward and extending into the colorless cuticle lining 

 the entrance to the pharyngeal bulb, its total length 0.288 mm. 



Radula very narrow, with a deep U-shaped groove. Teeth in 27 rows, the last 3 rudimentary. 

 Rhachis very narrow, naked. First pleural tooth (pi. xx, fig. 77) very large, upright, compressed, its 

 base quadrangular in lateral outline, the posterior border thin and overlapping the outer anterior 

 margin of the first pleural tooth of the succeeding row. Lower portion of the base rounded in front, 

 strongly thickened. Height of base about 0.210 mm., its length 0.114 mm. The anterior portion pro- 

 longed upward into a strong slightly curved hook about 0.180 mm. in length, upon the inner margin 

 of which is a series of 5-7 denticles midway of its length, decreasing rather irregularly in size from 

 abo\e downward. In the older, more anterior teeth of the radula, the number of denticles is occasion- 

 ally increased to 10-11, the lowest 4-5 being extremely small. Length of the largest denticles about 

 0.008 mm. 



The remaining pleurje, 5-tj in nundier, arc small and <if nearly the same size, oblique, the basal 

 portion thickened, the upper margin j)ortion prolonged posteriorly into a slightly flattened, bluntly 

 pointed hook with a thin, keellike plate below, the general shape resembling that of the fii'st pleural 

 tooth (pi. XX, fig. 78). Average length 0.05 mm. 



Hermaphroditic gland very thin, covering nearly all of the liver, its duct thin walled, slender, 

 about 0.6 mm. long by 0.1 mm. broad, arising from the right anterior lobe of the visceral mass near 

 the median line and passing in a short loop into its dilated ampulla. Anterior genital mass small, 

 plano-convex, its superior border occupied by the glandular portion of the vaginal duct, the sperma- 

 totheca, and the spermatocyst, its inner flattened face by the loops of tlie ampulla of the hermaphro- 

 ditic duct, its outer convex face formed by the nidauiental and albumin glands. The ampulla of the 

 hermaphroditic duct describes a short loop upon the inner face of the nidamental gland, passes for- 

 ward and upward, describing almost a complete circle, gives off the spermatic duct, and passes at once 

 into the nidamental gland. Length of ampulla .3 mm., its diameter 0.5 mm. 



The spermatic duct describes an 8-shaped loop closely attached to the anterior margin of the 

 genital mass, passes backward in a long free loop underneath the anterior end of the visceral mass 

 near the median line, returns upon itself, and passes into the penis. Total length about 8.5 mm., 

 diameter 0.2 mm. Penis cylindro-conical, 1 mm. long by 0.4 mm. wide, the retracted glans bluntly 

 conical, armed with very minute hooks, occupying nearly the whole length of the hollow pra'putium. 



The uterine duct (pi. xx., fig. 80, u. d.) is very slender and short, passing directly from the ante- 

 rior inner margin of the nidamental gland to its superior margin, where it receives the slightly wider 

 duct of the pear-shaped spermatocyst (0.5 mm. long) (pi. xx, fig. 80, sp. c), and passes immediately 

 into the spermatotheca. The spermatotheca (pi xx, fig. 80, -ip. Ih. ) is small, about 1 mm. in diameter, 

 spherical, and concealed entirely by the overlying portion of the vaginal duct. The total length of 

 the vaginal duct is about 7 mm., its proximal portion describing an S-shaped loop (pi. xx, fig. 80, a.), 

 and dilating rapidly into the glandular portion (pi. .xx, fig. 80, gl. ). This glandular jiart is thickened; 

 its walls of large gland cells, the lumen narrow; its total length about 1.2 mm. Its external surface 

 bears 4 equidistant longitudinal grooves, and the intermediate portions are transversely lobulated at 

 intervals, the general outline in cross-section being that of a quatrefoil. The distal portion of the 

 vaginal duct is nearly straight, about 4 mm. in length, and passes over insensibly into the vagina 

 (pi. XX, flg. 80, (!. d.). 



Habitat: Tide pools at extreme low water, near I'oint I'inns. Rare, but 4 specimens of this inter- 

 esting species having been taken. 



Araiilhodorts hudxoiti differs markedly in the detail.s of its radula armature, and also in the repro- 

 ductive system, from any other species of this genus, especially from the forms recorded thus far from 

 the Kacitic ccjast. Bergh (1880) has described Ac. inlosn var. alhesrois, and Ac. pilosa \a.T. purpurea, 

 together with a new species, Ac. ccerulescetis from -\laska. These are all strikingly different from .b-. 

 B. B. F. 190.i— 10 



