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



TJie Dorsal Lamina is narrow, and has the margin plain. 



TJie Tentacles are simple and numerous ; they are of two sizes, placed long and 

 short alternately. 



This is the smallest species of Styela in the collection, and there is nothing notable in 

 its external appearance (PL XIX. fig. 5). The test, which is comparatively thick, has a 

 little sand adhering to its outer surface, especially upon the left side. 



There are four folds upon each side of the branchial sac. They do not project much, 

 but have each about six closely placed internal longitudinal bars (PI. XIX. fig. 6, br.f.), 

 while there is only one bar in each interspace between two folds. The two rows of meshes 

 lying between two folds are transversely elongated, and contain each about six stigmata ; 

 they are occasionally divided by delicate horizontal membranes (PI. XIX. fig. 6). 



One specimen of Styela exigua was obtained at Port Jackson, Australia, in from 2 to 

 1 fathoms of water. 



Styela clava, Herdman (PL XIX. figs. 9, 10). 



Styela clava, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1880-81, p. 70. 



External Appearance. — This species is club-shaped, the pyriform body being supported 

 on a stalk of variable length ; it stands erect, and is not compressed. The anterior end is 

 narrow, but generally straight for a short distance ; from this the body widens rapidly for 

 the first two-fifths of its length, and then narrows more gradually in the remaining three- 

 fifths, the posterior end being prolonged into the stalk, which is generally about equal to 

 the body in length. The apertures are both at the anterior end ; they are four-cleft, and 

 more or less projecting, but minute and inconspicuous. The branchial is at the ventral 

 edge of the anterior end, and is directed ventrally ; the atrial is at the dorsal edge of the 

 anterior end, is more prominent than the branchial, and therefore more anterior, and is 

 directed anteriorly. 



The surface is very irregular ; the posterior half of the body and the stalk are creased 

 longitudinally, and the anterior half of the body is nearly covered by irregularly shaped, 

 but smooth and blunt knobs, mostly directed anteriorly. The colour is a dirty white, 

 with occasionally a slight yellowish tinge. 



Length (total), about 7 cm.; breadth (at broadest part of head), about 2 cm. 



TJie Test is tough but thin, and almost papery, except in the knobs and processes. 



TJie Mantle is very delicate, and is closely united to the test ; the musculature is very 

 feeble. 



The Branchial Sac has four narrow folds upon each side. The internal longitudinal 

 bars are rather numerous, about nine on a fold and twelve in the interspaces. The meshes 

 are transversely elongated, contain each six stigmata, and are occasionally divided trans- 

 versely by a narrow membrane. 



