TUNIC ATA. 15 



MOLGULA CONCOMITANS. 



(Plate v., figs. 1 A, and 2-7.) 



Localift/. — Wiuter Quarters, in McMurdo Bay. The single specimen measures : — 

 Length 2*5 cm., breadth 2 cm. 



External Appearance. — Body somewhat globular, rather flattened laterally, with a 

 straight anterior and a rounded posterior end. Apertures at the ventral an<l dorsal 

 edges of the anterior end, both on well-marked siphons, the atrial being the more 

 prominent (Plate V., fig. lA). The surface is not encrusted with sand, but has 

 small tag-like excrescences scattered over it, especially around the siphons. Colour 

 grey. 



Te.tt thin, cartilaginous, translucent ; prolonged into minute processes connected 

 with the vcasels of the test, and bearing o(;casional foraminifera or minute grains of 

 .sand, especially about the anterior end. 



Mantle yellow, opaque, and very muscular (fig. 4) — the sphincters being 

 especially strong. The mantle adheres closely to the test. 



Branchial Sac with seven folds on the right side and six on the left. There are 

 .seven bars on a fold, and one large, with several imperfect .smaller bars, in the 

 interspace. Stigmata not much curved, irregularly placed, varying considerably in 

 length (see fig. 5). 



Dorsal Lamina a short plain membrane. 



Tentacles, eight very large and much branched, with some much smaller ones 

 placed irregularly between. 



Dorsal Tuhercle large and simple, horseshoe-shaped, with the horns turned 

 inwards (fig. 6). 



Alimentary Canal ])ulky, intestine forming a narrow dark-coloured loop. 



Gonads large and yellow, a single sausage-like mass on each side. 



The single specimen of this species belongs to the group of Molgulids with a nearly 

 naked test, not covered with adhering sand and gravel. In this respect it resembles 

 ^f. citrina, M. nudu, }f. anipidloitles, and M. helleri from the Northern hemisphere, 

 and M. maxima and M. pedunculnta from Southern seas ; but it differs from all of 

 these in details of anatomy. It comes, perhaps, nearest to M. mixinut (described l)y 

 Profes.sor Sluiter from the 'Charcot' collection) ; and, in fact, it clo.sely reseni])lcs that 

 Antarctic species in extenial appearance and in several other respects. It diff"ers, 

 however, ncjtably in the mantle. Professor Sluiter describes M. maxima as having 

 the mantle feebly developed, with a feeble musculature ; whereas our specimen has an 

 extraordinarily strong and opa<]ue mantle, with conspicuous yellow muscles (fig. 4), 

 like tho.se of a ^ficrncosmus. The atrial siphon is the longer and narrower, the branchial 

 being short and wide. The large tentacles are extraordinarily bushy. 



The branchial sac, although agreeing in .some respects, such as tlic number of bar.'< 



