132 



CLASS M L L U S C A. 



SUB-CLASS G ASTEROPODA. 



ILLUSTRATIVE EXAMPLES. 



PLATE 4. 



DORIS. Body creeping, rarely floating, oblong, flat, convex, or sub- 

 prisraatical ; surrounded by a membrane from the head to the tail ; mouth 

 anterior and inferior, trunk-shaped ; tentaculse four, two anterior, placed on 

 the front of the body, retractile into a kind of calix or sheath ; anus on the 

 hinder part of the back, surrounded by the prominent gills ; gills lobed or 

 fringed ; aperture of the organs of generation placed on the right side. 



Cuvier, in the fourth volume of the " Annals of the Museum of Natural 

 History of Paris," has given a very extended account of the anatomy of this 

 genus, illustrated with several plates ; he has divided the genus into three 

 sections, according to the shape of the body : 



1. Body compressed, much larger than the foot. 2. Body subhemi- 

 spherical, bordering the foot. 3. Body subprismatical, the mantle edging 

 the foot. 



Illustrations : Doris trilobata, D. ladnata, D. nodosa, D. penrdgera, D. 

 limbata, D. tuberctdata, D. cornuta, D. atromarginata. 



OXCHIDORUS. Differs but slightly from the Doris. Body oval and 

 tumefied above ; foot thick, oval ; tentacular appendages four ; labial ap- 

 pendages ; mouth covered with a veil. 



This genus was established by Blainville, having separated it from the 

 Doris of Linnaeus and Gmelin. 



Illustration : Onchidorus Leachii. The foot of this species is overlapped 

 by the borders of the mantle, also the head when contracted ; its organs of 

 respiration consist of minute ramifications circularly arranged, and deposited 

 in a cavity at the posterior and mesial part of the back. The figure num- 

 bered 9 is a side view ; No. 10, the under surface. 



PERONIA. The body of this genus, like that of Onchidris, is tumefied 

 above, and oval or snboval in form ; the borders of the mantle overlap the 

 foot throughout its circumference ; tentacula two, and inferior ; labial 

 appendages two. 



Illustration : Peronia Mauritiana. The figure represents the animal from 

 below. The respiratory organ is situated in a cavity at the posterior region 

 of die back, and its external opening is by a rounded mesial orifice, pierced 

 at the inferior and posterior parts of the borders of the mantle. 



POLYCERA. Branchiae not expanded during repose, being covered by 

 two scales ; oval tentacula exceeding two in number ; body shell-less. 



Type of the genus, Doris flam (Montagu). One species, a native of the 

 western coasts of Britain. 



Illustration : Pdycera quadricarnis. 



TRITOXIA. Mouth terminal, and encircled with tentacules ; body oblong, 

 creeping, pointed behind, convex above, with the gills arranged along the 

 whole length of the back in form of scales, tubercles, or vascular tufts; 

 under surface flat or grooved. 



The form of this genus is parallelepiped, with the upper surface slightly 

 bagging throughout its whole length, the anterior extremity rounded, and 

 the posterior pointed. The back and sides are separated by two ridges, 

 forming four or five curves or festoons, with their convexity downwards, 

 and those which separate the sides from the foot are folded into much more 

 numerous curves. The mouth is placed anteriorly between the back and 

 the foot, covered by a wide, delicate, horizontal, semicircular, denticulated 

 membrane, and consisting of a longitudinal cleft, with a pair of lips ; 

 within it are a pair of curved horny jaws, compared by Cuvier to the shears 

 used for shearing sheep. The back is completely covered with round, 

 unequal, blunt tubercles, and at its fore part are a pah- of apertures, from 

 which the tentacules are projected, and in which they can be concealed ; but 

 they are not retractile, each forms a sort of crest, consisting of five processes, 

 and at their base the eyes are situated. From the edge of these apertures 

 the gills commence, and are continued along the upper ridges to the very 

 tip of the tail. The foot is rugous. Their habits have great resemblance 

 to those of the genus Doris. Whilst alive, their colours are generally 

 brilliant. Five or six species are known in the European seas, of which 

 the type is our 



Illustration : Tritonia Hombergti. 



TETHYS. Body fleshy, semitransparent, oval, tapering to a point pos- 

 teriorly, and terminating in front in a wide semicircular cloak, which, like a 

 sail with a fringed edge, covers and overlaps the head ; the mouth trunk- 

 shaped, and beneath the cloak ; two projecting tentacules above the base 

 of the cloak ; upper part of the body swelling, under part flat, and furnished 

 with a large foot ; anal and generative apertures on the right side ; branchiae 

 external, prominent, naked, tufted, and disposed in two longitudinal rows. 



This genus is remarkable for the large fringed cloak, which covering 

 overlaps the head, but contracting beneath forms a kind of neck. From 

 the funnel-shaped mouth can be projected a kind of cylindrical proboscis, or 

 trunk, with an aperture at its extremity. They are found in the Mediter- 

 ranean and the Adriatic. 



The type of the genus, of which two species are described, is the 



Illustration : Tethys Leporim (Gmelin). 



SCYLL.EA. Body gelatinous, oblong, greatly compressed on the sidos, 

 channelled beneath ; back with an elevated crest, with four alary processes 

 disposed in pairs ; branchiae external, expanded in fascicles over the internal 

 face of the dorsal processes ; head slightly prominent ; tentacula tw< >, 

 dilated above and narrowed towards their base. 



Illustration: Scyllcea pelagica. 



This is the type of the genus ; it inhabits the Atlantic Ocean. 



GLAUCUS. In describing this genus, authors have almost universally 

 placed this animal upon its back, so that they describe the right side for the 

 left, and vice versa, which occasioned them to think that the organs were 

 placed in a different manner from any other Mollusca. The animals of this 

 genus are very much altered by contraction in spirits. 



Their characters are: Animal long, subcylindrical, gelatinous, behind 

 attenuated ; head short ; mouth trunk-like ; tentacula four, the upper eye- 

 bearing ; gills fin-like ; lobed radiately, three or four pair on each side, 

 placed horizontally ; the orifices of generation and vent on the right side. 



Found in the Mediterranean, and other seas of warm climates, swimming 

 with great rapidity on the surface, in calm weather. 



Illustration: Glaucus Atlanticus. 



LANIOOENUS. Nearly allied to Edida. 



Body naked, long, alwve convex, beneath tlat, ending in a kind of tail ; 

 head rather distinct; tentacula four, small ; gill pectinate in a short row on 

 each side of the back ; described by a single specimen, collected by Sir 

 Hans Sloane, in the collection of the British Museum. 



Illustration : Lam'ogenus elfortianus of Blainville. 



EOLIS. Body oblong, creeping, ending behind in a point, rather convex 

 above, flat and channelled beneath ; mantle not distinct ; head short, with 

 four or six tentacula ; gills 

 prominent, in the form of 

 scale-like leaves ; papillae 

 or beards placed in longi- 

 tudinal rows along the 

 back ; orifice of generation Eolis. 



and vent on the right side. 



Blainville has proposed to divide this genus into two, keeping the name 

 ofEdis for all the species which have scale-like or papillary gills, and that of 

 Cavdina for those which have these organs in the shape of beard-like fila- 

 ments. 



1. ELOIDA. Gills scale-like. 

 Illustration : Elaida Cuvieri, E. Tergipes. 



2. CAVOLINA. Gills filiform. 

 Illustration : Cavdina perigrina. 



ORDER TECTIBRANCHIATA. CovBBKD-oiLLB. 



THKSK Gaotero|>ods, according to Cuvier, have the bronchia' 



along the right side, or back, in a leaflet form, and covered, more or less. 



by the pallium or mantle, in which a small shell is always contained. 



