352 



ScYLLjEA.- 



-MOLLUSCA.- 



-Pmeumobuanchiata. 



Genus Scyi.l^a. — The Scyllaas are oceanic, and 

 are found on floating sea-weed, the slender fronds of 

 wliich they seize by their furrowed or channeled foot, 

 being by this enabled to obtain a firmer grasp and 

 greater seonrity. — See Plate 6, fig. 1 [Sojllaa peluyica). 

 GknL'S Tethys. — The Tethyses are oceanic, attacli- 

 iiig themselves, like the Seylla\is, to floating sea -weed. 

 Tlieir broadly expanded head-veil, fringed with cirrhi, 

 gives them a peculiar look. One of them is mentioned 

 by Dr. Johnston, on the authority of Rapp, to be remark- 

 able, not more for its singular beauty than by its odour, 

 which is compared to that of roses. — See Plate C, fig. 1 

 [Ttlhys leporina). 



In a third series of this group (the Cerahrandiia of 

 Gray) the gills, which are placed, like the last, on the 

 upper surface of the mantle, are fusiform, papillary, 

 8im[]le, or branched. Such are the families Dcndro- 

 mitidcB, ProclouolidiV, Hervidce, Dotonula, Glaucida; 

 Eolididce, Fionidcc, and Hermmdce, examples of some 

 of which will be seen in Plate G. 



Genl's Glaucus. — The Glaucuses have slender, 

 cylindrical gills placed in tufts, proceeding symmetri- 

 cally from the sides of the body, and supported on broad 

 flattened footstalks. The animals are oceanic in their 

 habits, are predaceous, and are generally of a blue 

 colour. — See Plate 6, fig. 1 {Glaucus Athmlicus). 

 Dr. George Bennett informs us, in his "Wanderings," 

 that they feed greedily on the gelatinous Acalephs, 

 Velclte, and Porpitoe, animals always of a blue colour. 



and which are in consequence supposed to impart a 

 similar colour to their captors. Dr. Johnston gives 

 a good description of the Glaucus hcxtrpteri/gius, 

 a species from the Mediterranean. " The body," he 

 says, " glows with a fine cerulean blue colour, which 

 deepens in hue towards the ends of the fringes of its 

 ptero-liranchia;; the centre of the back is of a pearly 

 whiteness, bordered with a line of deep blue ; and the 

 sides are adorned with an interrupted series of fan-like 

 laciniated gills, by aid of which it swims reversed at the 

 surface of the Mediterranean Sea in numerous swarms." 



Family— EOLIDID^. 



The EoUds are generally elegant and beautifully 

 coloured creatures, and are active, constantly moving 

 their tentacles and extending and contracting their 

 papilla;.— (See Plate C, figs. 1-4.) They are often to 

 be met with swimming on the surface in an inverted 

 position ; but, generally speaking, they frequent rocks 

 at low water. Their chief food consists of Zoophytes, 

 but Alder and Hancock inform us that they have seen 

 the Flabellina punctata devour other Nudibranchs, and 

 even make a repast upon its own spawn. The spawn 

 of E(dis papulosa "forms an elegant spiral chain of a 

 milk colour, and several inches long, twisted upon itself 

 and constricted at regular intervals, so as to resemble 

 a necklace made of bugles." — [Johnston.) 



Oi:der III.— PNEUMOBRANCHIATA (= Pulmonata or Pulmonifeua). 



The air-breathing Gasteropods, containing the " Slugs" 

 and "Snails," are for the most part natives either of the 

 land or fresh water, a few only being found in salt 

 marshes or places near the sea. They are, with very 

 few exceptions, provided with a shell, both in their 

 yoimg or larval state, and when fully grown. They 

 have no gills, but breathe the atmosphere or external 

 air by means of a lung which is in the form of an air 

 sac or cavity placed on the front of the back, and lined 

 by a network of vessels. The air is admitted into this 

 cavity by an orifice in the side of the animal, which is 

 small and valve-like, and can be opened and shut at 

 pleasure. The young of the air-breathing Molluscs 

 undergo no metamorphosis, but when first hatched are 

 shaped like the parent, and are not furnished with 

 cephalic fins. They are hermaphrodite animals, the 

 sexes being united in each individual. They are 

 usually active and well organized, having a distinct head 

 furnished with teeth, jaws, well-developed eyes, and 

 tentacles. They have a broad foot upon which they 

 ci eep, and the great majority of them possess a large, 

 spiral shell. In this latter respect, however, they dificr 

 considerably — some genera of slugs having only small, 

 concealed shells, flat, and partially membranous; other 

 sings having the shells rudimentary and granular, while 

 a few have none at all. The tongue, or lingual mem- 

 brane, is short and very broad, often nearly as wide as 

 liiUg; and the teeth are very numerous, similar, with 

 broad bases, and invariably arranged in transverse rows, 



giving the appearance of a tesselated pavement. The 

 greater proportion of these animals are herbivorous, 

 living upon land plants and vegetables; and in these 

 the teeth are all similar in form, with broad bases and 

 dentate crowns. Some, however, are carnivorous, and 

 in these the teeth are slender, and more or less pointed 

 or barbed at the extremity. " The mode in which the 

 tongue is used may be seen by placing a Lymnea or 

 Planorbis in a glass of water, inside which the green 

 conferva has begun to grow ; they will be observed 

 incessantly cleaning off this film. The upjier lip, wilh 

 its mandible, is raised; the lower lip, which is horse- 

 shoe shaped, expands, the tongue is protruded and 

 applied to the surface for an instant, and then with- 

 drawn ; its teeth glitter like glass paper, and in L}'mnea 

 it is so flexible that frequently it will catch against 

 projecting points and be drawn out of shape slightly as 

 it vibrates over the surface." — [Woodward.) The shell 

 of the Pulmonata is not secreted on the exterior of 

 the mantle, as in other Gasteropods (see p. 185). 

 "Gegeubaur draws attention to the fact that the first 

 rudiment of the shell in Limax, Clausilia, and proba- 

 bly Helix, is not secreted on the exterior of the mantle, 

 as in other Gasteropoda, but is deposited, in the form 

 of calcareous granules, within its substance." — [Huxley.) 

 The " Slugs " and " Snails " are universally distributed 

 over the globe, but are of a large size, and more numer- 

 ous individually in warm, moist, intertropical countries, 

 and are especially abundant in large, well wooded 



