38 BRITISH TUNICATA. 



Colon-)/ polymorphous, semi-cartilaginous [or gela- 

 tinous], sessile. Individuals immersed, irregularly 

 arranged into several subcircular [or elongate] 

 systems without common excretory orifices. Thorax 

 and abdomen rather distant, united by a peduncle. 

 Apertures terminal, both with six lobes. Branchial 

 sac with papillae. 



The individuals of this genus greatly resemble those 

 of Diazona in form, but differ in being wholly 

 immersed in the common mass, which is generally 

 depressed or incrusting. 



1. Distoma rubrum Savigny. 

 (Figs. 106 and 107.) 



Distoma rulirum SAVIGNY [in Descr. Egypte, Hist. Nat. I 

 (dated 1809, hut later), pt. 2, p. 24, and] Mem. Anim. 

 sans Vert, pt. 2 [(1816), pp. 38, 177], pi. iii, f. 1, and 

 pi. xiii ; [LAMOUROUX Exp. meth. Polyp. (1821), p. 72, 

 pi. Ixxvii, f. 1 ; THOMPSON in Ann. Nat. Hist. (1) V (1840), 

 p. 95, and in Rep. Brit. Assoc. for 1843 (1844), p. 264;] 

 FORBES & HANLEY Brit, Moll. I [1848], p. 18, pi. A, f. 6, 

 and pi. B, f. 6 ; [COCKS in Rep. R. Cornw. Polyt. Soc. for 

 1849 (1850), p. 74; GOSSE Man. Marine Zool. II (1856), 

 p. 33, f. 48;] THOMPSON Nat. Hist. Ireland, IV [(1856), 

 p. 361 ; MERRIFIELD Nat. Hist. Brighton (1860), p. 81; 

 NORMAN in Zoologist, XVIII (1860), p. 7247]. 



\_Polyzona rulra FLEMING Philos. Zool. II (1822), p. 513, and 

 Moll. Anim. (1837), p. 211.] 



[Distoma rubra Risso Hist. nat. Europe merid. (1826), IV, 

 p. 278; ANSTED & LATHAM Channel Isl. (1862), p. 219.] 



\_Synoicum rubrum COLDSTREAM in Edinb. new Philos. Journ. 

 IX (1830), p. 239, pi. ii, ff. 8-11.] 



\_Distomus ruber OKKN Allgem. Naturgesch. V, 1 (1835), 

 p. 94 ; LAMARCK Hist. nat. Anim. s. Vert. ed. 2, III (1840), 

 p. 498; H. & A. ADAMS Gen. Recent Moll. II (1858), 

 pi. cxxxv, ff. 4, 4 o.] 



Colon)/ (fig. 106) an erect, compressed mass of a 

 reddish-violet colour. Individual* (fig. 107) slightly 

 prominent, yellowish, scattered over the two sides in 

 groups of from three to twelve in each system. Aper- 

 tures a little apart, 6-lobed, tinted with purple. 



