32 BRITISH TUNICATA. 



Section 1. Without common excretory orifices. 

 A. Branchial aperture only -with lobes. 



Genus 19. DIDEMNUM Savigny. 



Didemnum SAVIGNY Mem. Anim. sans Vert. pt. 2 (1816), 

 p. 194; [LAMOUROUX Exp. ineth. Polyp. (1821), p. 75;] 

 MILNE EDWARDS Obs. Ascidies comp. [1841], p. 79, [in 

 Mem. Acad. Sci. List, France, XVIII (1842), p. 295]. 



Didemnium* WOODWARD Man. Moll. [pt. 3 (1856)], p. 341; 

 [H. & A. ADAMS Gen. Eecent Moll. II (1858), p. 602]. 



Colony sessile, gelatinous or cartilaginous, [sometimes 

 thin] and incrusting. Indi.ti duals dispersed irregu- 

 larly over the surface, or very indistinctly combined 

 into systems, without a common excretory orifice. 

 l>i-<n'liitd iiftrftnTe with six lobes, atrial plain, indis- 

 tinct. [Tentacles eight in number.] Thorax short, 

 sub-globular ; abdomen larger than the thorax and 

 united to it by a peduncle more or less distinct. 

 Ovari/ single, placed at the side of the abdominal 

 cavitv. 



V 



1. Didemnum gelatinosum Milne Edwards. 

 (Figs. 101-103.) 



Didemnum gelatinosum MILNE EDWARDS Ohs. AscMies comp. 

 [1841], p. 79, [in Mem. Acad. Sci. Inst. France, XVIII 

 (1842), p. 295,] pi. vii, ff. 5, 5 a-d; [DESHAYES in Cuvier's 

 Regne Anim., Moll. (dr. 1845), pi. cxxix, f. 4; THOMPSON 

 in Ann. Nat. Hist, (2) I (1848), p. 64; VICTOR CARUS in 

 Proc. Ashmol. Soc. II (1851), p. 268; M. SARS in Nyt 

 Mag. f, Naturvid. VI (1851), p. 153;] THOMPSON [in Rep. 

 Brit. A'SSOC, for 1852 (1853), p. 293, and] Nat. Hist. 

 Ireland, IV [1856], p. 364 ; [WOODWARD Man. Moll, pt, 3 

 (1856), p. 341, pi. xxiv, f. 10 ;] M. SARS in Forhandl. 

 Vid.-Selsk. Christ. 1858 [1859], p. 66; [GEGENBAUR in 

 Arch. f. Anat. 1862, p. 149, pi. iv; ALDER in Rep. Brit. 

 Assoc. for 1866 (1867) p. 208 ; GRUBE in Abli. schles. 



* So spelt in the authors' MS. and by several others, but this variation 

 in spelling is not here discriminated in the synonymy of the various species. 



