OPISTHOBRANCHIATE MOLLUSCA FROM MONTEREY BAY. 149 



Glans? penis (retracted) with an armature of extremely small hooks along its canal for O.r. mm., in 

 about 15 rows, the indivi<lual hooks 0.004 mm. high. 



Habitat: On hydroids and bryozoa in tide pools near Pacific Grove; rare. But eight individuals 

 have thus far been taken. Graceful and slow in movement, rather active in continement, frequently 

 swimming at the surface. 



Type no. 181280, U. R. National IMuseum. 



Geuns 16. HOPKINSIA .Alac-Farland. 

 HopUnsia MaoFarland. op. cit., p. 53. 



Form of body elongate-oval, very much depressed; the notieum thickly set with long papilhe, 

 simple or occasionally forked; pallial margin not set off from the sides of the body but sloping 

 gradually down into the foot without any distinct boundary, anteriorly continued into a broad velar 

 expansion formed by the fusion of the labial tentacles in front; rhinophores nonretractile, perfoliate, 

 Ijranchise several, separate, simply i^innate plumes, arranged in a horseshoe-shaped arc; the foot 

 broad, its margin thin, undulating, in front deeply emarginate, behind forming a short, broad, blunt 

 tail. Head broad, its tentacles very broad and thin, auriculate at the outer posterior angles, in front 

 united into a veil with undulating margin. 



Labial armature a ring of very short, thickened rods. 



Radula very narrow, the rhachis naked; the first pleural tooth long, erect, hooked, the outer one 

 flattened, horizontal, denticulate. 



The genus Ifopkinsia is perhaps more closely related to Idalia than to any other of the Goniodo- 

 ridinie. Tliat it forms a valid genus distinct from the latter I have not the slightest doubt, having com- 

 pared the Mediterranean representatives of Tdalia with it in detail. As to external features a compari- 

 son of figures 24 and 25 of plate xiv with the excellent figures of Alder and Hancock (Monog. Brit. 

 Xudibi-. Moll., Fam. I, pis. 20 and 27) or of Bcrgh (Ueber die Gattung Idalia, Arch. f. Naturgesch. 

 xi.vii, 1, 1881, pi. VIII, figs. 1 and 2) shows most striking differences in the general body form which 

 serve to distinguish the genera at sight. The body is very low, not high; the dorsum wide, not 

 narrow; the sides of the body very gently inclined, not abruptly sloping; the pallial margin indis- 

 tinguishable, not conspicuous; the tail short and rounilcd. net long and lanceolate; the dor.sal papillaj 

 and the undulating marginal veil of the head and inodilicil tcnta.li.s are all different. Details of the 

 internal anatomy, notably the pharyngeal and repniilu(ii\r a|.paiatus, strengthen the conchision. In 

 an extended morphological study of this genus, which 1 have in preparation, I hope to take up the 

 question of its relationships in detail. 



This new genus is dedicated to Mr. Timothy Hopkins, through whose generous appreciation the 

 foundation of the Hopkins Seaside Laboratory was rendered possible. The type of the genus is the 

 following species. 



20. Hopkinsia rosacea MacFarland. 



[PI. XXXI. liKs. J4, 2.'S; j.l. XXI, ligs. 97-103.] 

 Ikipkiima rnsarm MacFarland, op. cit., p. .i4. 



General body outline elongate-elliptical (pi. .\x.xi, fig. 24), sometimes elongate-oval or almost quad- 

 rangular (pi. XXXI, fig. 25), the ends abruptly rounded. Body firm, fragile, the many spicules rendering 

 it almost calcareous, much depressed, the dorsum but slightly arched above and sloping gradually 

 outward to the thin margin of the foot, there being no trace of a pallial margin nor ridge marking the 

 boundary between back and sides. 



Foot (pi. XXXI, fig. 25) broad, abruptly rounded behind into a broad and short tail, in front deeply 

 incised by a broad, triangular notch, the margins of which are slightly thickened, the remaining 

 margin of foot and tail thin and undulating. 



Head broad, its tentacles very broad, united in front, forming a veil-like expansion with undu- 

 lating margin, the rounded posterior angles slightly auriculate and free from the anterior outer margin 

 of the foot for but a short distance. The mouth a longitudinal slit. 



Dorsum thickly set everywhere with long, gently tapering, soft papillje (pi. xxxi, fig. 24), many 

 reach'og a length of one-half to two-thirds that of the whole animal. The tips of these papilUe are 

 usually pointed and simple, but in nearly every individual branching forms may be found. The 

 branching may Vie limited to a bifid apex, or the branch may arise along the side. In many cases this 

 branching is due to a fusion of two or more papilla. ( pi. xxi, fig. 97) . PapilUe most abundant on lateral 



