COMMON si:a-snail. 



289 



(■Mil scarcely i)e regarded as a valid one — and ap- 

 ]n-(>aclies the t'ulh' tadjKilc-likc f'oi'in of the (ail whicli lic- 

 lungs to the speciincns just mentioned, which ai'c I'ar 

 from the commonest, even in Spitzljcrgen. The pecu- 

 liarity of the caudal fin, on the other iiaiid, in this 

 species is its smaller length, whicii varies between 1 1 

 and II % (occasionally rising, however, to 16' ., %) of 

 the length of the liodv, or lictwccii lO and 65 % ot 

 that of the head. The adhesixc disk f(ii'me<l 1>\' the 

 ventral tins is also less than in the preceding species, 

 its length never rising to \., that of tiie head, and 

 sometimes sinking as low as to 36 % thereof. It is some- 

 times surrounded e\cn in front by the pectoral fins, a 

 dermal tla|) uniting the latter to each other — tliis is 

 distincth' the case, for example, in a specimen from 

 Bravik (a iirth of the Baltic Sea), and also in one of 

 LCtken's figures of ('ifdof/asfrr luihiieii tVom Kara Sea 

 — hut in this S])ecies as in the preceding one, there 

 is generalh an inter\al between the ])ectoral fins. The 

 position of the \('nt varies considerably: in a young 

 specimen 28 nun. long, from Stor Fjord (Spitzbergen), 

 which, however, still retains distinct traces of the larval 



of a uinform gray or red, dotted with brown. In Cy- 

 chif/dsfer Fahricii the black peritoneum generally shines 

 through. Lepechin's specific name {lineatus) is derived 

 fi'ora a variation of colour common in this s])ecies too, 

 wdicre the markings of the b(jdy are arranged in longi- 

 tudinal, undulating streaks. In short, Ave may find 

 every conceivable variation and transition between uni- 

 coloured, dotted, sjjottcd and streaked forms, light or 

 ilai'k, reddish oi' grayish, yellow ov cxen blue \arieties. 

 CoLLETT, indeed, gives ten of these dift'erent forms. As 

 in the ])receding species, however, these variations of 

 colour belong chiefly to the younger specimens. The 

 vai'icty remarked by Mal.ai (sfellatus), with star-shaped 

 chromatophores in the skin, is also marked (Plate XV, 

 fig. 10) by a St. Andrew's cress of" sepia-coloured streaks 

 from the eye. This marking is parti}' represented in 

 one of v. Whk air's two figures, and may also occur, 

 according to Hanssox, in the preceding species. 



The Common Sea-Snail is of especial interest in 

 the geology of Scandinavia and Finland during the pe- 

 riod immediately preceding that knoAvn by geologists 

 as the Recent or Human. Its occurrence in the Baltic 

 stage, the vent lies close to the beginning of the anal is one of the relics collected by S. Lovex, of the qua- 

 fin; in a specimen ,53 mm. long, from the same loca- \ ternary, northern connexion between this sea and the 

 lity, the distance between the vent and the anal fin is Arctic Ocean. The species has received greatest pro- 



of that l)etween the latter and the ventral disk; 



minence from Ekstr(")m'.s description of it, under the 



and in a specimen 60 mm. long, from the neighbour- name of Lipuiis harhatus", as occurring in the island- 

 hood of Visby ((rothland), the former distance is % of I belt of Morko, where he found specimens 130 mm. 

 the latter. In ordinary cases, however, the vent lies long. Far up in the Gulf of Bothnia, too, this species 

 about half-way between the ventral disk and the anal fin. attains a length of at least 90 mm., for one of the 

 The coloration is essentially the same as in the specimens in the Royal Museum', which was taken by 



o 



preceding species, and is no less variable. In full-grown Mr. Abom off Neder-Kalix, is 94 mm. long. According 



specimens, however, at least in Sweden, it is usuallj^ to Mela it occurs both in the island-belt of Abo and 



darker, the ground-colour being more distinctly tinged off the island of Hogland in the Gulf of Finland, 

 with gray; and the brown dots are more often collected \ Lindstrom assigns it to Gothland, and has presented 



into transverse bands on the fins and the bod\. These to the Royal Museum a male 60 mm. long, from the 



bands are in most cases very irregular, as is shown in neighbourhood of Visby. In the south of the Baltic, 



V. Wrights two figures of Scandinavian specimens however, it was unknown until Theel and Tkybom 



(Plate XV, figs. 7 and 9), and in a colour- variety com- during the voyage of the gunbout Gunhihl, in July, 



nion in the Arctic regions, the transverse bands are 1878, took a small specimen 19 mm. long, south of 



interrupted at the middle of the sides and their superior Ystad, and some other small specimens, the largest of 



and inferior parts are set alternately opposite the spaces which was 26 mm. long, between Moen and Arcona. 



between them, a dark band from the back lying verti- All these last specimens were found at a depth of 10 



cally above a lighter band from the anal side and vice or 11 fathoms, among stones and sea-weed on a sandy 



versa. The lielly itself, on the other hand, is usualK bottom. Off Kiel it does not occur, according to Mo- 



" This specific name is derived from the beard-like lower lobe of tlic pectoral fins, and as early as 1785 Bi.ocH had given ihe spe- 

 cies the name of Der Hartjiscli, Vyclopterus pinna pectorali barbiformi. 



* A female with almost ripe roe, taken at the end of April (1842). 



Scandinavian Fti^htit 



37 



