128 THE VOYAGE OF H.M.S. CHALLENGER. 



in appearance. Minute rather distant projections on the outer surface give it a finely 

 roughened appearance. The projections are slightly larger, and more numerous on the 

 lips of the apertures. 



The peduncle is hollow, but has the cavity crossed by delicate trabecular formed by 

 prolongations of the thin test on each side. The matrix is homogeneous, but is traversed by 

 irregularly running delicate fibres. Small rounded protoplasts are scattered through it ; 

 but there are no bladder cells nor pigment corpuscles, and no vessels are visible. The outer 

 surface, especially of the papillary projections, is covered with adhering foreign particles, 

 diatoms, &c. 



The Mantle is very thin, and adheres closely to the inner surface of the test. The 

 musculature is feeble, the bundles being narrow and distant ; they are of a light brown 

 colour, and form a wide-meshed delicate network. 



The Branchial Sac is a wide-meshed coarse net with several folds on each side. The 

 transverse vessels are wide and all of one size. The internal longitudinal bars are strong, 

 and are only present on the folds, which are formed of three bars closely placed and united 

 by short transverse ducts. In each interspace between the folds, but not placed symmetri- 

 cally, there is a fine longitudinal vessel joining the transverse bars. The meshes formed 

 by the folds and the transverse vessels are square or slightly elongated transversely. 

 The internal longitudinal bars are cihated on the sides, but not on the internal thickened 

 edge. 



The Endostyle is conspicuous. It is of a brown colour, and has prominent lips. 



TJie Dorsal Lamina is a plain broad membrane. 



TJie Tentacles are compound. They are large and considerably branched, but few in 

 number. 



The Alimentary Canal lies on the left side of the branchial sac, towards the ventral 

 edge and posterior end. It is a long and narrow tube, with no distinct stomach. 



The Genital Glands are two in number, one on each side of the mantle. 



This is a most interesting form, on account of its evident relationship to Cideolus, as 

 shown by the shape and position of the apertures, the place of attachment of the peduncle 

 to the body, and especially in the structure of the branchial sac. The most striking- 

 difference from Cideolus, and in fact from all the other Bolteninae, lies in the peduncle, 

 which in the present species is evidently merely a short prolongation of the body (PI. 

 XIII. fig. 7), covered by test in the normal condition ; while in all the species of 

 Cideolus the structure of the test on the long thin peduncle is modified so as to give it 

 the appearance of being a distinct organ attached to the body. Otherwise the external 

 appearance is quite that of a Cideolus. The branchial aperture is anterior, just at the 

 dorsal side of the peduncle, while the atrial is nearly posterior (PL XIII. fig. 7). 



The test is thin, and its outer surface is slightly papillated, while the lips of the trian- 

 gular branchial (PI. XIII. fig. 8) and bilabiate atrial apertures are rough, with rather larger 



