<;•_> THE VOYAGE OF H.M.S. CHALLENGER. 



There are two species in the genus, Ascopera gigantea with a large body and a short 

 peduncle, and Ascopera pedunculata with a small body and a much longer peduncle. 



Ascopera gigantea, Herdman (PL I., PI. II. figs. 1-4, and PI. III. figs. 3-5). 



Ascopera gigantea, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1880-81, p. 238. 



External Appearance.- — The shape is somewhat pyriform, and not compressed laterally. 

 The anterior end is wide, truncated, slightly cleft in the centre, and ends in a siphon at 

 each extremity. Behind the siphons the body swells out into a globular form, attaining its 

 greatest width at about two-fifths of its length from the anterior extremity; it then narrows 

 to become the wide peduncle constituted by the posterior two-fifths. The edges are both 

 convex, but the dorsal is more so than the ventral, especially towards its posterior end. 

 The animal is attached by the lower (posterior) end of the stalk. 



The apertures are both at the anterior end ; they are distant, conspicuous, tubular, 

 and prominent. The branchial is at the end of a projection from the ventral edge of the 

 anterior end, in the form of a wide tube bent round posteriorly so as to present a convex 

 surface anteriorly and an open mouth posteriorly. The aperture is large and funnel- 

 shaped, and is bounded by six wide, low, undulated lobes separated by slight clefts. The 

 atrial aperture is placed at the summit of a projection from the dorsal edge of the 

 anterior end. This projection is larger than that on which the branchial aperture is 

 placed, and extends further forwards, thus rendering the atrial aperture more anterior 

 than the branchial. The aperture is wide, quadrangular, and directed anteriorly. 

 It is bounded by four lips with slightly undulated edges. 



The surface of the body is even, there being no projections or marked irregularities. 

 It is not, however, perfectly smooth, being finely roughened all over. 



The colour is a pale yellowish grey-green, with a slight tinge of brown towards the 

 lower end of the peduncle. 



Entire length (antero-posterior), 30 cm. ; length of peduncle, 10 cm. ; greatest breadth 

 ,(across apertures), 15 cm. ; breadth in middle of body (dorso-ventral), 12 cm. 



The Test is thin and almost membranous, but tough. It is semi-transparent, and is 

 slightly roughened externally, but quite smooth on the inner surface. 



The Mantle is delicate and membranous, with a few distant rather strong muscle bands 

 running transversely over about the anterior half of the right side and the left side ; they 

 are only absent on the dorsal part of the left side and the posterior end. At the posterior 

 end of the body, where the peduncle commences, the mantle is firmly united to the test, 

 even after immersion in alcohol. 



The Branchial Sae is extremely thin and delicate, and has seven folds on each side; 

 those next the endostyle are rather slighter than the others. The internal longitudinal 

 bars are wide but delicate. The transverse vessels are also wide, and all of one size. The 



