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



surf. temp. 78°'2. They measure 2-2 cm., and 1'8 cm. in length. They agree in all 

 respects with Traustedt's description and figures. A third specimen of the same form, 

 measuring 1"8 cm., is amongst the specimens mounted as microscopic slides during the 

 expedition. It is from the same locality. 



Salpa inuscuhsa, n. sp. (PI. VI. figs. 1-4). 



External Appearance. — The shape is elongated, with the anterior and posterior ends 

 somewhat abruptly narrowed. The middle part of the body tapers slightly towards the 

 posterior part, and is ridged longitudinally. The apertures are both terminal. The 

 branchial is large, and has semicircular lips. The atrial is smaller and more circular in 

 outline. It has no prominent lips. The surface is smooth. The colour is a yellowish 



gi"ey. 



Length, 4 cm. ; greatest breadth, 1"2 cm. 



The Test is thin, and only moderately firm. It is fairly transparent. 



The Mantle has a well-developed musculature. There are ten very wide muscle 

 bands, which nearly [touch one another, so as to form almost a complete muscular 

 investment. 



The Endostyle is conspicuous. 



The Dorsal Lamina has the ribbed portion rather narrow. 



The Dorsal Tnhercle is large but simple. It is elongated antero-posteriorly. 



The Visceral Mass is of moderate size. It is placed near the posterior end of the body. 



Localities. — (1.) April 12, 1876; Station 351, Atlantic, off the West Coast of 

 Africa ; surface ; lat. 9° 9' 0" N., long. 16° 41' 0" W. ; surf. temp. 8r-8 ; two specimens. 



(2.) April 13, 1876; Station 352, lat. 10° 55' 0" K, long. 17" 46' 0" W. ; surf, 

 temp. 77°'7 ; two specimens. 



This species resembles the solitary form of Salpa hexagona somewhat in shape, in 

 the position of the apertures, and especially in the musculature, but differs from that 

 species in several points of structure, and particularly in the total absence of the large 

 posteriorly-placed spines found in Salpa hexagona. 



The body is somewhat prismatic in shape (PL VI. fig. 1). The dorsal and ventral 

 surfaces are flat, and are bounded by prominent ridges, while the sides of the body are 

 (in the spirit specimens) rather depressed. There are thus four longitudinal ridges, a 

 dorsal and a ventral on each side of the body. In the specimens examined, a transverse 

 section of the middle of the l)ody would have a quadrangular shape with projecting 

 angles (PI. VI. fig. 2). In the solitary form of Saliva hexagona there are six longi- 

 tudinal ridges. , 



The anterior end of the body is wider than the posterior (PI. VI. fig. 1), and passes 



