194 ARioN suBFrsrrs, 



Diagnosis. — Avion suhfuxcus may be distinguished from A. ater, the 

 species with which it is most liable to be confounded, by its smaller size, 

 flatter and shorter rugosities, less uniform colouring, whitish sides, and the 

 presence of dark lateral banding on the body and shield ; the foot-fringe 

 is also usually whitish or yellowish grey, with dark though less regular 

 lineolation than in A. ((tcr, and the animal cannot assume the hemis- 

 pherical shape when at rest which is so marked a feature of that species. 



In the juvenile stage the affinity with A. ater is even more striking, but 

 in the latter species the rug.ii are invariably more elongate and separated 

 by bluish interstices ; moreover, in A. subfuscus the body is always 

 comparatively longer when at rest, and there is always more or less 

 orange slime on the shield, which is absent in the larger species ; the body 

 also is always darker than the shield, whereas in A. ater the coloration is 

 usually more perceptibly uniform. 



Inteenally, this species is separable from its congener by the different 

 point of fixation of the oviducal retractor, and by the constant and marked 

 inflation of the free oviduct, an inflation quite unlike the gradual basal 

 enlargement in Arioii /lortenais, or the bulbous expansion of the vestibule 

 in Arioii (iter, while there is usually a large flesh-coloured mass or ruffle 

 at the base of the albumen gland. 



Description. — Animal of medium size, re.aching eighty milliineties in length 

 when adult ami fully e.vtended, of a dull uniform dusUy-brown above, ochieous sub- 

 dorsally, becoming whitish towards the sole, witli a more or less distinct blackish 

 or black longitudinal band at each side, extending over body and shield ; BODV 

 TUBERCLES moderately pronounced, finer, slendei-er, and flatter than in Arioii ater, 

 and nowhere fused into longitudinal ridges, with about twenty-five longitudinal 

 series on each side ; shield attenuated in front, broadly rounded and almost trun- 

 cate behind, shagreened, with lyre-shaped dusky, longitudinal marking, arching the 

 respiratory orifice and becoming less distinct beliiml ; RKSPIRATORV ORIFICE round, 

 sliglitly angulated below to the anal cleft, which is directed forwards ; head 

 usually somewhat darker than the body ; NECK pale, with four parallel longitudinal 

 furrows, two continuing to the foreliead, while the outer grooves reach the dusky 

 ommatophores ; LOWER TENTACLES capped witli brown ; sole indistinctly tripar- 

 tite, pale yellowish-white, tinged «ith brown towards the tail, and minutely beset 

 with milk-white points, mid-area slightly more transparent ; foot-fringe pale 

 yellowish-grey, lineolated similarly to Arion ater, but less regularly and more 

 faintly, and scarcely continued over the side-areas of the sole. 



Dermal-Mucus occasionally almost colourless but generally of a pale yellow, 

 or when scalded, of an orange colour, and usually most dense on the anterior part 

 of the mantle and near the caudal gland ; that emitted by the tail-gland is ropey and 

 almost colourless ; LocoMOTORY-Mucus colourless, but stained by admixture with 

 the dermal secretion. The yellow colour of the body appears to be often due to the 

 slime, as when this is removed after scalding, the skin is almost invariably dnll 

 greyish or greyish-lirown. 



The Shell may be at times wholly absent, or quite vestigial, and represented 

 only by amorphous granular white matter, which solidifies in drying. 



Internally, the walls of the body-cavity are grey, densely beset with milk- 

 white limey particles. The supra-pedal hland is imbedded in the tissues, ami 

 visibly extends for about three-fourths of the 

 total length of the body. The Bi'CCAL fJAN(iLIA i^ita.a^^.a^f' 



are oblong with a short commissure ; the J^^^^^^'i^'\,^ „ f"^- 209.— 

 suPRA-ffiSOPifAcJEAL ganglia are opaque-white '^^ — '"^"^-^fc;;- /J^„l ^sul/mcls 

 anteriorly ; the suB-(ESOPiiA(iEAL group are vvT"*^"^^"^^/ (much enlarged), 



intimately fused together. The undivided "^^^"^-'Ci^ (Christchurch, 



AORTA is four or five mill, long, of an opaque- "^^^i^M^I^^ Alif^di 

 white colour, as are all the arterial branches, // " M|\\ 



rendering them very conspicnous over the 



stomach, liver, and other dark internal organs. The otoliths are very numerous, 

 of a mi)re broadly oval shape than in A. horteii^it, and ofteji with a central speck. 



