Genus 6. POLYCERA,* Cuvier. 



Corpus limaciforme, aut lseve aut tuberculatum, postice acuminatum, vix palliatum. Caput 

 subinferius, subtentaculatum, velo frontali mucronato vel tuberculato, in lineam dorsalem tuberculatam 

 utrinque continuato ; maxillis corneis. Tentacula 2 dorsalia, subclavata, laminata, non-retractilia. 

 Branchice plumosse, in linea media dorsi anum circumdantes, appendicibus linearibus vel lobatis utrinque 

 ornatse. Apertura genitalis ad latus dextrum. 



With great uniformity in general appearance, the Polycerina shew so many varieties in 

 detail that it is difficult to avoid raising almost every species to generic rank. The genus 

 'Polycera was instituted by Cuvier, in the ' Regne Animal,' on the type' of the Doris quadrilineata 

 of Midler, a species of which, though reappearing from time to time under many different 

 names — cornuta,Jlava, lineata, varians, and typica — still remains the only animal in which the 

 Polyceral (many-horned) character of the frontal expansion is distinctly recognisable. Several 

 other species have been included in the genus, nearly all of which have since been detached to 

 constitute different genera, and the two which form our second section might without impro- 

 priety be raised to a similar rank, were it not that we are unwilling to multiply genera on 

 slight characters. The most available characters for generic distribution in this sub-family 

 are the tentacles — laminated or unlaminated — sheathed or unsheathed — with or without basal 

 filaments. The appendages adorning the branchial region are also of importance ; as well as 

 the more or less distinct cloak, sometimes only indicated by a dorsal area circumscribed by a 

 ridge of tubercles or filaments, and occasionally almost entirely wanting. Cuvier thouo-ht 

 that the branchial lobes covered and protected the branchiae in times • of danger, but most of 

 these appendages are but ill adapted for such a purpose. 



Themisto of Oken is synonymous with Polycera. The range of the genus is rather uncer- 

 tain, but it appears to extend throughout the European seas, and probably over most of the 

 shores of the Atlantic. Five species have been found in Norway, two in France, and one in 

 the Mediterranean. Of extra European species, one occurs in the Canary Islands, another on 

 the coast of. North America, and a third in Rio de Janeiro. 



The body of Polycera is limaciform, smooth or tuberculated, swelling a little in the centre, 

 and acuminated behind. The head is subinferior and has the sides a little lobed or dilated 

 without forming true oral tentacles. The mouth is furnished with corneous jaws, a rare cir- 

 cumstance in the Doridida. The veil, as it is usually called, or, more properly, the frontal 



* From ttoXvq, many, and tcipaq, a horn. 



