RETORT ON THE TUNICATA. 75 



and the posterior end are strongly convex ; the body is attached by the extremity of the 

 produced ventral edge. The sides are slightly convex. 



The apertures are both on the wide anterior end. They are sessile, and not con- 

 spicuous ; the branchial is at the ventral edge of the anterior end just above the stalk ; 

 it is indistinctly six-lobed, and directed anteriorly and slightly ventrally ; the atrial is 

 at the dorsal edge of the anterior end, it is distinctly four chft, and directed dorsally and 

 a little anteriorly. 



The surface is even, but finely roughened all over with a minute granulation. 



The colour is white with a hyaline tinge. 



Length of the body (antero-posterior), 4 cm. ; breadth (dorso-ventral), 5 cm. 



The Test is cartilaginous, thick and strong. It is smooth and glistening on the inner 

 surface. The texture is very compact, and no vessels are visible. 



The Mantle is not very thick. The muscle bands are irregular, they are distinct but 

 distant. The branchial and atrial siphons are well developed. 



The Branchial Sac is not thick, and has seven folds upon each side. The internal 

 longitudinal bars are strong ; there are usually about six on a fold, and several in the 

 space between two folds. The transverse vessels are variable, and sometimes irregular; 

 horizontal membranes are usually present. The stigmata are arranged in irregular 

 transverse rows, rarely in spirals. 



2 he Dorsal Lamina is short, but very wide ; it is thin, and there are no ribs nor 

 marginal teeth. 



The Tentacles are large, branched, about twelve in number, and of two sizes placed 

 larger and smaller alternately. One very large one occurs at the ventral edge, just anterior 

 to the extremity of the endostyle. 



TJi e Dorsal Tubercle is situated a long way posterior to the tentacular circlet ; it is 

 equidistant from the branchial and atrial siphons, is somewhat reniform in outline, and 

 is elongated antero-posteriorly. The horns are simply turned in, not coiled ; the opening 

 is directed dorsally and to the left. 



This species is very unlike a Molgula in external appearance, and would much more 

 readily be referred to the Cynthiidas at first glance, while in some respects it appears to 

 have affinities with Ascopera. The position of the stalk is peculiar (PI. V. fig. 1). 

 It is a prolongation of the ventral edge, and is more anterior than posterior ; hence, in 

 the natural position of the animal, the atrial aperture is higher and more prominent 

 than the branchial. There are no hair-like processes on the outer surface of the test, 

 and no incrusting sand, but the surface is finely granulated all over. 



The mantle is not very muscular, the bundles being rather distant (PI. V. fig. 2). 

 There are circular bands on the prominent branchial and atrial siphons, from each of which 

 a series of radiating bundles issues. The edge of the branchial siphon is indistinctly 

 six-lobed, while the atrial is square (PI. V. fig. 2). 



(ZOOL. CHALL. EXP. — PAET XVII. — 1882.) li 11 



