328 MAKIJAL OP THE MOLttJSCA. 



sinuses in tlie skin^ from wMch. it returns to tlie auricle "by two 

 lateral veins, without haying circulated through the gills. The 

 heart is contained in a pericardium to "which is attached a small 

 Ventriclej or portal heart, for impelling blood to the liver ; the 

 hepatic veins run side by side with the arteries and open into a 

 circular vein, surrounding the vent, and supplying the gills. 

 Only hepatic blood, therefore, circulates through the gills. In 

 ^olis there are no special gills, but the gastro-hepa.tic papillae 

 are accompanied by veins which transmit blood to the auricle. 

 The skin acts as an accessory breathing-organ ; it performs the 

 function entirely in the ElysiadcB, and in the other families, when 

 by accident the branchise are destroyed. The water on the gills 

 is renewed by ciliary action. The fry is provided with a trans- 

 parent, nautiloid shell, closed by an operculum, and swims with 

 a lobed head- veil fringed with cilia, like the young of most 

 other gasteropods. (Hancock and Embleton, Phil. Trans. 1852. 

 An. Nat. Hist. 1843.) 



Family YI.— Dorid^.* Sea-lemons. 



Animal oblong; gills plume-like, placed in a circle on the 

 middle of the back ; tentacles two ; eye -specks immersed, 

 behind the tentacles, not always visible in the adult ; lingual 

 membrane usually with numerous lateral teeth, rachis often 

 edentulous ; stomach simple ; liver compact ; skin strengthened 

 with spicula, more or less definitely arranged. 



DoBis, L. 



Etymology-, doris, a sea-nymph. 



Example, D. Johnstoni, PL XIII. , Fig. 1. 



Synonyms, Dendrodoris, Eb. Hemidoris, Strp. 



Animal oval, depressed; mantle large, simple, covering the head 

 and foot; dorsal tentacles 2, clavate or conical, lamellated, retrac- 

 tile within cavities ; gills surrounding the Vent on the posterior 

 part of the back, retractile into a cavity ; head with an oral 

 veil, sometimes produced into labial tentacles ; mouth with a 

 lower mandible, consisting of two horny plates, united near 

 the front, and having 2 projecting points ; lingual teeth nume- 

 rous, central small, laterals similar, hooked and sometimes 

 serrated, 24-68 rows; 37-141 in a row; nidamental ribbon 

 rather wide, forming a spiral coil of few volutions (p. 41, 

 Pig. 29). 



* Contracted from Dorididce ; as the Greeks used Deucalides for Deucaliontiades. 

 Ehrenberg divided the genus Doris into sections by the number and form of the giUs, 

 characters of only specific importance. 



