1880.] NATURAL SCIENCES OF PHILADELPHIA. 101 



the middle, with its free margin tuberculated or digitate. The frontal 

 veil is continued in a more or less tuberculated ridge, that limits the true 

 back, and posteriorly ends in a single strong or in several smaller 

 dorsal (branchial) appendices on the outside of and behind the region 

 of the gill. The true back with longitudinal rows of more or less 

 developed connected tubercles, sometimes forming low longitudinal 

 ridges. The number of leaves in the club of the rhinophoria is not 

 large. The gill is composed of a moderate number (five to seven) of 

 leaves, which are either simply pinnate or composite (bi- or tripinnate). 

 The tentacles are small, flattened or auriculate. The jaws or man- 

 dibular plates in form somewhat recall those of the u^olidiidce, strong, 

 flattened, sometimes with a peculiar superior process. The rhachis of 

 the radula naked ; on the pleura? two large hook-formed lateral teeth, 

 of which the outer is much larger than the inner ; at the outside of 

 the laterals are four to eight, somewhat flattened uncina^. A large 

 prostate gives the genital apparatus a particular feature ; the arma- 

 ture of the penis is of the usual kind. 



About the biological relations of Polycera very little is known, as 

 usual among the Nudibranchiata. The spawn of the most common 

 northern species is known, and a part of the developmental history 

 has been investigated by Ray Lankester.' 



A small number of species have been described by different authors 

 in the course of years. Alder and Hancock (Monogr. part T, 1855, 

 p. 45, XVIII) established and rather well characterized two groups 

 of Polycera ; according to these authors Gray soon after (Guide I, 

 1857, p. 213) denominated these groups Polycera (typical) and Palio, 

 which perhaps might be conserved as subgenera. 



L POLYCERA (stricte). 



Marge limbi frontalis digitatus. Folia branchialia simpliciter pin- 

 nata ; appendices dorsales (branchiales) singula? majores. 

 Lamellae mandibulares processu superiori aliBformi. 



1. F. quadrilineata (O. F. Miiller). M. Atlanticum ; Mediterraneum. 



2. P. horrida, Hesse. Joum. de Conchyliol.,3 S., XIII, 4, 1873, p. 345. M. 



Atlanticum. 



' Ray Lankester, Contrib. to the Developm. hist, of Moll., Philos. 

 Trans., MDCCCLXXV, p. 29, PI. 10, f. 1-9. 



Meyer and Moebius have, moreover, given a figure of the shell of the 

 embryo of their Pol. ocellata (1. c, fig. 10 j. 



