■22S 



ARION CIRCUMSCRIPTUS. 



placed very forward on the sliicld, wliich is entire ; mucus pore \'ery distinct, above 

 the tail ; the young' are white or straw coloured, with Ijlackish liead and tentacula. 

 Habitat: Moist meadows, hedgebanks, etc., common. 



We have found it very uniform and constant in its character, though it may 

 po.ssibly be the Arioji iiicr in an immature state. — G. Johnston, Edinb. New Phil. 

 Journal, ISiilS, \(il. v., p. 76. 



Description. — Antmal of the Ariim shape, but stouter especially when contracted 

 and with a much softer skin than its close ally, virion /wrtcii'^ls ; about thirty mill, 

 in length when adult and fully extended ; of a [lale creamy-grey colour, darker 

 grey dorsally, but shading to M'liitish towards the friuge ; a l)lack and sharply- 

 delined lateral band extends the whole length of the body on each side, beneath 

 wliich is sometimes an indistinct orange band, formed by ]iigment cells breaking 

 througli the skin ; there is a slight mid-dorsal icmcL when young, wliich, however, 

 gradually disapjiears during growth, but its place is almost inwariably indicated by 

 a line of pale mid-dorsal TUliliUCLES, which contribute to form a pair of dorsal or 

 inner bands ; .siUKLD granulose and bluntly rounded at both ends, bearing a dis- 

 connected continuation of the longitudinal body banding ; nODV TUBERCLES rather 

 long and slender ; SOLE opaque, waxy white, and indistinctly tripartite, the median 

 portion slightly darker and more transparent than the side areas, and occupying 

 more than one-third of the width of the body ; FOOT-frinoe broad and white or 

 pale-grpy in colour, usually without perceptible lineolations, but sometimes the 

 lineoles are clearly pigmented, especially at the caudal end of the body. 



The SHErj, is, as is usual in the genus, represented by a layer of limey-paste, but 

 is sometimes found in the form of one or more solid lime particles of variable size. 



Internally, the sciPR.v-CESOPiiAdEAL ganglia 

 are very conspicuous, and united by a .slender com- 

 missure, which, unlike Arion ttfci-, is not opaque-white 

 or enlarged medially as in that species. The body 

 cavity is whitish and therefore does not display so 

 strikingly the exquisite lace-like network of milk- 

 white arteries and arterioles, a whiteness due to the 

 dense investment by lime particles of their outer 

 sheaths, and which renders them so conspicuous in the 

 dark form ot A. afn- ; the aorta is large and white, 

 and runs 4 to ."> mill, before its bifurcation, the Mdiite 

 investment commences abruptly, as no part of the 



VKNTKiLMJi is white; the otooonfa are very numerous, 



central speck, and comparatively broader in proportion than those of A. hortensis. 



The curiiALR' uictractohs resemble those of Arion 

 hortensis. The broad and flat TENTACULAR muscles 

 have their roots four to five mill, apart to the right 

 and left of the kidney, but are not quite symmetrical, 

 either as to position of roots or whltli of muscle. 

 The liraucl\ to the lower tentacle arises at about 

 half the total length. The l'lLVi;YN(iEAL retractor 

 distinct, and usually dividing about half-way into two 

 slender branches, which are lixed to the buccal bulb ; 

 the root arises about three mill, liehind the kidney, 

 about a millimetre to the right of the median line, and 

 though sometimes broad the muscle is on the whole 

 much nari'ower than the tentacular retractors. 



The RKPJiODUcriVE organs display an oval or roundish ovotestis, with rela- 

 tively large follicles, very dark in colour, especially in the interstices, the whole 

 being completely imbediled in the LIVHK ; the UEUMAPHlioniTE DUCT is rather 

 long and slender, but scarcely sinuous; ALnuMKN GLAND very large ami broad, 

 of a dirty semi-transparent yellow ; ovispKiiMATODUCT thick and very stiffly 

 Hexed; OVIDUCT yellowish and very broad ; si'Urm DUCT or prostate composed in 

 the upper part of small, longish, and somewhat separated follicles ; free oviduct 

 short, and of uniform whlth ; EPIPHALLUS stiff', and not very slender, gradually 

 enlarging downwards, but without the bulbous base of ^1. /mrtciisi-s, and shewing the 

 internal fohls tli)-ough its substance as white longitudinal lines ; VAS DEFERENS 

 rather long ; SPELiMATHECA inversely spatulate, the stem short and thickening 

 downwarils; AiiauM very long, somewhat constricted and uniform in width, with 

 a cimspicuous yellow glandular investment, 



Fig. 232.— Nerve centres of 

 Arion circuniscriptus (greatly 

 enlarged). Christchurch, 



Hants. S., Mr. C. Ashford). 



oval in shape, with a 



Fig. 233. — Cephalic retractors 

 o'i Arion ciTcuinscriptus X 4. 



(Christchurch, Hants. S., Mr. 

 C. Ashford). 



