M O L L U S C A. 



619 



both as similar. The salivary glands are placed on each 

 Me the gullet, and empty their contents behind the 

 jaws. The gullet has a few longitudinal folds, the 

 stomach is simple, scarcely different from the gullet, 

 and the intestine proceeds almost directly to the anus, 

 situated on the right side. The liver is small and si- 

 tuated behind, enveloping the stomach, and intimately 

 united with the ovarium The organs of generation 

 exhibit nothing remarkable. The pedunculated resi- 

 de has a simple canal. The external opening of the 

 organ* of generation is situated a little before and be- 

 neath the anus. 



The following species are natives of the British seas. 

 1. Tri'.otiia a>borescent. Length about an inch. 

 Margin above the mouth, with four plumose appen- 

 dage*. Foot narrow, eides compressed. Cloak smooth, 

 soft, with five or six plumose tubercles on each side, 

 decreasing in size towards the tail. Tentacula two, 

 fathered, contained in a sheath. 



Thi* species is described and figured by Cuvier, in 

 hi* Mrmoire itir la Scylltf, p. 27. tab. 1. fig. 8, 9, 10. 

 We hive found this species in the Zetland isles, agree- 

 ing with the characters of Cuvier, with this difference, 

 that the branchiff in his are only five, while in ours 

 they appeared to be six on each side. But as the two 

 posterior ones arc very small, and as his examples were 

 preserved in spirits, it is probable that they have escap- 

 ed detection. 



9. Tritonia pbinatifida. Length three-tenths of an 



inch. Tentacula filiform, inserted in a trumpet-shaped 



sheath. Branchiie in a single row on each side, ovnte, 



of grey papilla- with black lips arranged in 



flre or six whorls. 



Fint described and figured by Montagu, Linn, 

 Trn$. vol. vii. p. 78. tab. vii. fig. 2, 3. 



S. Tritonia bijtda. Length about a quarter of an 

 inch. Tentacula (sheath ?) two, broad, erect, and bifid, 

 behind which are two eyes. Branchi.T in a single row, 

 on each side, orate, pedunculated, unequal ; opposite 

 pairs equal, summit semitransparcnt, uniform on the 

 surface, but complicated within. 



I -'. observed by Montagu. Linn, Tram. vol. xi. 

 p. 198. tab. xiv. fig. S. 



M. Curier has separated from the genus Tritonia 

 such species as possess four tentacula ; two superior 

 and two at the anterior extremity of the body. The 

 branch:? are placed in transverse rows along the sides 

 and back. He likewise state*, that there is no cloak, 

 or rather no marked division between the cloak and 

 the foot. This genus he has termed Eoiida. Unfor- 

 tunately none of the characters which are here selected 

 appear to mark any particular plan of organization ; 

 and the species to which he refers, differ as widely from 

 one another as they do from the Tritonue. Three of 

 hu references are to British species, which we shall 

 ixrw describe. In all of these the branchizc are simple, 

 neither in the form of imbricated processes, nor plumes. 

 V Tritonia papillota. Length nearly three inches. 

 Anterior tentacula, smooth, superior ones annulated. 

 Middle of the back smooth, sides thickly set with coni- 

 cal lengthened branchiae, which, when closely examin- 

 ed, appear to be disposed obliquely in rows, containing 

 about ten in each. 



* From the points of the papillae, (says Montagu,) 

 an extremely mcid secretion ii discharged, that some- 

 time* envelopes the whole animal." We have observed 

 it PO**" the horny jaw* of a Tritonia. 



This species is not uncommon at different parts of 

 the coast. It was probably first observed at British by 



Turton, who appears to refer to it in his British Fauna, Mollutea 

 under the name Doris vermigera. It is described and """ "Y~" 

 figured by various authors, particularly by Baster, 

 Opusctda 'Subseciva, i. p. 81. tab. x. fig. 1. A. B.C. I). 

 Muller, Zoolooia Danica, tab. cxlix. fig. 1, 2, 3, -i. 

 Montagu, Linn. Trans, vol. xi. p. 16. tab. iv. fig. S. 



5. Trilonia plumosn. AVe have observed in Zetland 

 this small species, which is about half an inch in length. 

 It resembles the preceding in form, but has only one 

 row of simple branchiee on each side. The superior 

 tentacula were pinnated towards the summit. The an- 

 terior ones simple. Opportunities for a more minute 

 examination did not occur. The structure of the su- 

 perior tentacula forbid us to regard it as the young of 

 the T. papillosa. 



C. Irilonia ctcrnka. Length about a quarter of an 

 inch. Tentacula simple, with eyes behind the superior 

 pair. Branchia- clavate in transverse rows on the back. 

 Two oval vesicles on the right side, between the second 

 and third row of branchia. 



Described by Montagu, Linn. Trans, vol. vii. p. 78. 

 tab. vii. fig. 4, 5. 



7. Tritonia loygicornis. Length half an inch. An- 

 terior tentncula about half the length of the body ; the 

 superior pair short, with the eyes behind. On the 

 right side, near the eyes, a cluster of short papillae. 

 Bronchia- on the back in four transverse rows. 



Described by Montagu, Linn. Trans, vol. ix. p. 107- 

 tab. vii. fig. 1. 



It is probable that the cirri on the right side, in this 

 and the preceding specie*, mark the anus, and furnish 

 a character for a generic distinction. 



8. Tritonia pedal a. Length about half an inch. The 

 four tentacula tubclavated and wrinkled, with eyea 

 behind the superior pair. Branchia' in four fasciculi, 

 imperfectly connected transversely. Foot with two 

 fleshy lobes in front. 



This species, is described by Montagu. Linn. Trans. 

 vol. xi. p. 197. tab. xiv. fig. 2. 



IV.TEBOIPES. This gcnuswasinstitutedbyCuvier for 

 the reception of those species which have only two ten- 

 taculn, and a single row of branchiae on each side, which 

 act likewise as suckers, and enable the animal to crawl 

 on the back. Forsthal described one species in his 

 Descriplionei Animdium, p. 99. as Limax tergipes. The 

 species may be distinguished by the number and form 

 of the branching 



1. Tergijxt macutata. Length about a quarter of an 

 inch. Tentacula filiform, retractile, with a tntmnet- 

 shaped shenth. Branchiae nine on each, and consisting 

 of a clavate sheath, with a sexpartite margin, a concave 

 summit, with a single papilla in the centre. 



Described by Montagu. Linn. Tram. vol. vii. p. 80. 

 tab. vii. fig. 8, 9. 



V. THETHYS. This genus is characterised by a row Thsthys. 

 of branchiaf on each side the back, and a large mcni- 

 branitceous expansion above the mouth, bearing two 

 tentacula towards its base. 



This genus was first instituted by Litmeus, but it is 

 to M. Cuvier that we owe the discovery of its most im. 

 portant characters. 



The body is ovate, with the cloak and foot continu 

 *us. The neck is distinct from the foot, and is narrow. 

 Above, the neck is continuous with the clo;k, from 

 which arises a large semicircular expansion, which the 

 animal probably uses as a fin. The margin of this expan- 

 sion is fringed with numerous filaments, and on the up- 

 per surface, within the border, is a row of conical tuber- 

 cles. The true tentacula are placed towards the base of 



