BY II. LEIGHTON Kl STEVKN. 289. 



■might not be preferable to propose a new genus. In view of the 

 fact that the number of siphonal lobes may vary within other 

 genera (cf. Ascidia decemplex Sluiter) I have tliought it better to 

 adopt the present course. 



This species is named for my wife. 



MOLGULA MORTONI, Sp.nOV. 



(Plates XXV., figs. 4 5; xxvi., fig.8; xxvii., figs.ll-12). 



External appearance (PI. xxv., fig.5). — The shape is roughly 

 ovoid. Length 23, breadth (dorso-venti^l) 27, thickness (lateral) 

 17*5 mm. The anterior surface is domed, its even surface being 

 ■broken by the prominences on which the apertures are situated, 

 and by a ridge between these. The left side and tlie two ends 

 are evenly convex, the right side is flattened; it was attached to 

 a plank by this side. The colour is a dark grey passing into 

 dusky tan in the neighbourhood of the siphons, and on the ridge 

 between them. The branchial aperture is six-, the atrial four- 

 lobed. 



The test is moderately thin but comparatively opaque, and 

 leathery; on the inner side it is white and has a satin sheen. 

 The external surface is devoid of processes and sand-grains, and, 

 but for very small closely placed pustules on the siphonal areas, 

 is smooth or only slightly wrinkled. Test-cells are very numerous; 

 they are of elongate-fusiform shape. Around the widely separated 

 vessels are clustered cells of irregular shapes which are possibly 

 phagocytes. The ectoderm adheres to the test, and comes away 

 in patches attached to its inner side. Peculiar cell-clusters, 

 ■resembling solid morula embryos, are also present in the test. 



The mantle is strong and opaque, its opacity being largely due 

 to the presence of a black pigment. Muscle-fibres are present in 

 abundance arranged quite irregularly, no definite bands being 

 formed. The alimentary canal and gonads are deeply imbedded 

 in the mantle, and therefore visible through it (PI. xxvii., fig 11). 



Tlie branchial sac (PL xxvi., fig.8) bears seven strong folds 

 on either side, whose relation to endostyle, dorsal lamina, and the 

 two apertures, is shown diagrammatically by fig. 1 2, Pl.xXvii. The 

 26 



