150 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
HOLO HEPATIC A. 
Phanerobranchiata. 
POLYCERIDAE. 
Polycerella davenportii sp. nov. PI. 1, figs. “2-7. 
Body limaciform, slightly constricted behind the rhinophores. Length 2- 
4 mm. Breadth (when creeping) about £ of length. Color dirty green, 
speckled with black and splashed with sulphur-yellow around and on rhino¬ 
phores. Mantle distinct, without marginal flap, not covering the foot which 
is pale yellowish and long in extension posteriorly where it tapers evenly to 
a notched point. Anterior angles of foot moderately prolonged as oral palps, 
anterior margin usually salient. Rhinophores long (in extension £ length of 
body), heavy, clavate, simple, contractile, not foliate, laminate, or retractile, 
without sheaths. Gills three, small, rudimentary in appearance, dorsal, me¬ 
dian, each consisting of a recurved stem bearing three posteriorly directed 
branches between which is stretched, in perfect specimens, a delicate web. 
The middle gill is set on the very conspicuous pulsating cardiac prominence 
and shows scarcely any branching, the web being thicker than in the lateral 
members. Occasionally a single rudimentary fourth branch anteriorly directed 
appears. Dorsal papillae not on edge of mantle, usually one pair in front of, 
one at level of, and one behind the gills. Two smaller pairs form a posterior 
rosette. Papillae small length of contracted rhinophores), inconspicuous. 
Mouth anterior, funnel-shaped, dorsally exposed in extension, armed with 
thin mandibular lamellae. Anus, a transverse slit, median, dorsal, just behind 
and under gills. Radula almost as in P. emertonii Verrill (’80-81, p. 887 ; ’82, p. 
548), rhachidian tooth wanting; pleurae strongly hooked with accessory points, 
large ; uncini two, sickle-shaped. Formula 2-1-0-1-2. 
This odd little sea-slug is most nearly related to P. emertonii 
Verrill (’80-’81, p. 387 ; Bergh, ’83, pi. 9, figs. 1-6 and pi. 8, 
figs. 9-19), which it resembles in general organization, color, size, and 
dentition and from which it differs in dentition (slightly), in the 
fewness and smallness of the papillae and the relatively much larger 
rhinophores, in the fact that the webbed gills are simply and singly 
pinnate instead of simply but doubly (alternately) pinnate, in the 
shape of the gills and number of their branches (which is much 
greater in P. emertonii), and finally in the character of the foot which 
in P. emertonii is covered by the mantle. Professor Verrill’s oyeat 
