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EXPLORATION OF ALASKA. 
Limbus frontalis digitatus vel tuberculatus. Branchia 5—7-foliata. 
Appendices dorsales (extrabranchiales) 1-3. Tentacula brevia, lobi- 
formia. 
Lamelle mandibulares laterales fortes, sat applanate. Radula 
rhachide nuda; pleuris dentibus lateralibus hamatis duobus (margine 
levi), interno minore, externo majore, et dentibus externus 4-8. 
Prostata magna; pleuris ut in omnibus Polyceratis. 
The genus Polycera was established by Cuvier (1812?), to receive 
the Doris quadrilineata of Miller and (in 1830) allied forms ; a few 
years afterwards (1815°, and not knowing the genus of Cuvier, Oken 
formed his Themisto, nearly identical with the Polycera of Cuvier.* 
The Cufea of Leach (1852), is entire y congeneric with the genera 
of Cuvier and Oken, as is also very likely the Phanerobranchus of 
A. Fridol (Moquin-Tandon). The Zimacia of O. Fr. Miller (1781), 
contains a whole series of different Nudibranchiata, among them the 
D. quadrilineata, and, as first-named species, the D. verrucosa; the 
name cannot therefore be employed here. 
Although, through Cuvier and Alder (1841), their external char- 
acters were somewhat made known, still Polycera, like so many 
other Nudibranchiata, remained very superficially known, until the 
large monograpb of Alder and Hancock,! that first really unveiled 
their external and internal structure, although Frey and Leuckart? 
had given some anatomical notices of these animals. Lately more 
light has been spread over the northern species of the group, through 
the investigations of Meyer and Moebius,’ and of G. O. Sars.‘ 
The true Polycera shows a form of body common to the whole 
family. The well-developed frontal margin is more or less curved in 
* A careful search has failed to find any other ground for supposing that 
Cuvier described the genus Polycera in 1812, or at any date before 1817, so 
that the 1812 of Hermannsen is almost certainly merely a misprint. The 
name Themisto, of Oken, if congeneric, sbould therefore take precedence. 
—DALtu. 
1 Alder and Hancock, Monogr. Brit. Nudibr. Moll., Part 2, 1846, fam. 1, 
Pl. 23; Part 4, 1848, fam. 1, Pl. 24; Part 5, 1851, fam. 1, Pl. 22; Part 6, 
1854, fam. 1, Pl. 17 (anat. !); Part 7, 1855, Pl. 46 supplem. figs. 20, 21. 
2 Frey and Leuckart, Beitr. zur Kenntn. wirbellose Thiere, 1847, p. 66- 
70, taf. i, fig. 12, 18. 
3 Meyer and Moebius, Fauna der Kieler Bucht, i, 1865. p. 49-57, m. 2 
taf. und taf. iv, A, B. 
* q. O. Sars, Moll. reg. arct. Norv., 1878, p. 312, 3818, Tab. xiv, fig. 14-16. 
