168 Mr. J. Alder on the British Tunicata. 



Thylacium variegatum, n. sp.? 



Body (in each individual) transversely ovate, depressed, doridi- 

 form, shaded with flesh-colour and red. Apertures not much 

 apart on the upper surface, the branchial rather nearer the end. 

 Test slightly wrinkled, or nearly smooth, generally red towards 

 the anterior, and paler towards the opposite end, with a paler 

 raised circle round each aperture, that of the branchial largest, 

 and radiated with red. Tentacular filaments linear, stout. 

 Branchial sac with folds. The individuals are connected by a 

 membranous expansion at the base, of a paler colour. Length 

 (transverse) of individuals about one-eighth of an inch. Diameter 

 of the general mass one-half to three-quarters of an inch. 



One or two specimens of this curious species were kindly sent 

 me by Mr. Jeffreys, along with other Ascidians, from Lulworth 

 Cove. I am much inclined to believe that this is the true Di- 

 stomus variolosus of Gsertner, judging from the figures copied 

 in Blainville's ' Manuel de Malacologie/ which greatly resemble 

 our Ascidian, the only material difference being that the aper- 

 tures are represented six-cleft. On turning to Gsertner's de- 

 scription, quoted in Savigny^s ' Memoire,^ p. 38, we find it to 

 agree even more closely with this species. The individuals 

 {verrucce seu tubercula) are " ovalia et ex croceo rubra," and the 

 apertures are surrounded by a swollen margin with six rays, 

 ** quasi in tot discissus fuerit denies." If we may understand this 

 to apply to the coloured markings, giving the apertures the ap- 

 pearance as if cut into six segments, the description agrees with 

 what is seen in the branchial aperture of the Lulworth-Cove 

 specimens, which have the paler area surrounding it often di- 

 vided into rays like the leaves of a flower ; these rays are fre- 

 quently six, though the aperture, which is small and inconspi- 

 cuous when closed, is obscurely quadrate. Should this conjec- 

 ture prove correct, Gsertner's Distomus has been entirely mis- 

 understood by Savigny, as the present species has no relation- 

 ship with the genus Distoma of the latter, founded upon the 

 species he has so well described under the name of D. rubrum. 

 Further investigation, however, is necessary; and the suggestion 

 is now thrown out to induce naturalists who may meet with 

 this Ascidian in a living state to examine it more carefully. 



The specimens sent by Mr. Jeffreys are parasitical upon the 

 test of Cynthia mammillaris, another lost species of Gaertner 

 which has been already alluded to. 



I lately received from Mr. George Hodge specimens of a Thy- 

 lacium that may possibly be identical with this, though rather 

 larger and of a deeper red. They were found on the fronds of 

 Laminaria digitata cast ashore at the Island of Herm. 



