Genus 4. jEGIRUS,* Lov^n. 



Corpus robustum, gibbum, postice attenuatum, vix palliatum, tuberculis validis, prominentibus 

 undique instructum. Caput inferius, subtentaculatum, maxilla unica superiore. Tentacula 2 dorsalia, 

 cylindrica, simplicia, intra vaginas retractilia. Branchiae plumosse, in linea media dorsi anum circum- 

 dantes. Apertura genitalis ad latus dextrum. 



; Professor Loven established this genus in 1844, in the ' Proceedings of the Royal Swedish 

 Academy,' for a curious little mollusk, the Polycera punctilucem of D'Orbigny, at present the 

 only known species. Its most striking characteristic is the large wart-like tubercles with 

 which it is covered, but it differs from Polgcera, and apparently from all the known genera of 

 the Dorididce, in having smooth, unlamellated tentacles ; and instead of having two lateral 

 jaws, as in several of the other Nudibranchs, it has a single dorsal one, a character in which 

 it resembles the land slugs. 



The body of JEgirus is stout and rather gibbous, tapering to an obtuse point behind. It 

 is studded with large and prominent tubercles, which extend over the whole of the upper 

 surface. There is no distinct cloak, but the rudimentary margin of one maybe readily traced, 

 projecting over the head in front, and running along the sides of the body to the branchial 

 plumes. The head is inferior, and has on each side a flat tentacular appendage. There is 

 only a single jaw, which forms an arched corneous plate on the upper side of the mouth. 

 The two dorsal tentacles are linear and smooth, and are retractile within lobated sheaths. 

 The branchiae are plumose, surrounding the vent on the median line about one third down the 

 back. They are protected anteriorly and laterally by large lobed tubercles. The foot is 

 nearly linear, square in front, and obtusely pointed behind. The aperture of the sexual 

 organs is on the right side. 



In internal organisation, JEgirus resembles Polycera as closely as it does in external form : 

 there are, however, some very interesting modifications of detail, particularly in respect to the 

 buccal armature. 



The mouth opens on the under surface of the head, and the channel leading to the buccal 

 organ is very short. This latter organ is firm and muscular, but rather small : it is furnished 

 with a single horny plate or jaw (PI. 17, fig. 14 d, and fig. 15), situated in the buccal lip 

 above, holding exactly the same position, and apparently acting in the same manner as 

 the horny jaw or tooth of Limax. This is the only instance among the Nudibranchs in which 

 we have detected an upper jaw. It is lamelliform, rounded above, and has the lower or cut- 

 ting margin, which projects downwards, truncated, thickened, and produced' into an obtuse 

 point in the centre. The orifice of the buccal organ is guarded below by two lateral fimbri- 

 ated membranes (fig. 14 e), angulated above. The tongue is broad, as in Boris tuberculata, 

 having nineteen rows of amber-coloured, simple, compressed spines, thirty-eight or forty in 



* From iEgir, the god of the Ocean, in northern mythology. Professor Loven originally wrote the 

 name of the genus JEgires, but in a more recent publication he has changed the termination to us, 

 which we adopt as more consonant with classical usage. 



