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



has been already seen in several species of Styela (e.g., Styela oblonga and Sty ela flaw*). 

 Tiny are represented in this sac by four closely placed internal longitudinal bars (PI. 

 XXII. tig. 2, br.f.), forming meshes which contain each one stigma only. 



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

 bars are broad and ribbon-like, and bound rather wide series of meshes, of which there are 

 three rows in each interspace. Each mesh contains six or seven stigmata, and occasionally 

 narrow transverse bars are present, crossing them for short distances. The tentacles are 

 numerous and very delicate. Each of the polycarps on the inner surface of the mantle 

 is somewhat flask-shaped (PI. XXII. fig. 3, g.), and has a funnel-like duct at the 

 narrower end. The walls of this genital mass contain scattered rod-shaped calcareous 

 spicula (PI. XXII. fig. 4, sp.), rather like those found in the test of Cynthia complanata. 



One specimen of Polycarpa minuta was dredged in the Antarctic Ocean (to the south 

 of Kerguelen Island), at Station 150 ; February 2, 1874 ; lat. 52° 4' S., long. 71° 22' E.; 

 depth, 150 fathoms; bottom temperature, 1°"8 C. ; bottom, rock. 



Polycarpa molguloides, Herdman (PL XXII. figs. 5-7). 



Polycarpa molguloides, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1880-81, p. 76. 



External Appearance. — The body is transversely ovate, or sub-cylindrical ; it is 

 elongated dorso-ventrally and depressed ; and is attached by the wide posterior end. The 

 apertures are distant, they are both on the anterior end (upper surface), and are incon- 

 spicuous. 



The surface is entirely covered by a thick layer of sand, shells, &c. The colour is dark 

 brown. 



Length (antero-posterior), 3 cm.; breadth (dorso-ventral), 7 cm.; thickness (lateral), 

 4 cm. 



Tlie Test is moderately thick and leathery ; it is covered with branched hair-like 

 processes, to which the sand-grains, &c, are attached. 



The Mantle adheres closely to the test ; it is thick and rough, and the musculature 

 is feeble. 



Tlie Branchial Sac has four folds upon each side. The transverse vessels are nearly all 

 of one size, but occasionally a larger one is met with. There are six internal longitudinal 

 bars on the folds, and four in the interspaces. The meshes are transversely elongated, and 

 contain each twelve stigmata. 



Tl>e Dorsal Lamina is a plain membrane. 



The Tentacles are numerous and crowded ; they are all of one length, and are of a dark 

 brown colour. 



This is a very remarkable species, and is exactly like a Molgula in external appearance 

 (PI. XXII. fig. 5), the body being entirely covered with a thick coating of sand and 



