TUNICATA. 9 



representation of the species, as known to me, than does the ' Charcot ' fig. 57 ; that 

 the dorsal tubercle is more coiled and has the horns proportionately larger (cf. our 

 fig. 4), than is shown in the ' Charcot ' fig. 37 ; that Prof. Sluiter's text-figure of the 

 branchial sac on p. 41 scarcely does justice to the marked differences between the 

 transverse vessels which he describes on the following page (cf. our fig. 6, tr. tr', tr"), 

 and that the stigmata are in our specimens much more elongated than he shows. 

 Other minor differences will be found on comparing the details of the two descriptions, 

 but still it cannot be doubted that both refer to the same species. 



I may add that this species was obtained in much greater quantity by the Scottish 

 Expedition in the ' Scotia ' at the South Orkneys. 



HALOCYNTHIA DISCOVERYI. 

 (Plate IV., figs. 6-12.) 



Locality. Winter Quarters, in McMurdo Bay. 



External appearance. Body wide and low, somewhat flattened, with the two 

 apertures far apart on prominent siphons attached by posterior end. Surface irregular, 

 much wrinkled; colour yellow-brown. Size: 2'5 cm. dorso-ventrally x 1'5 cm. 

 antero-posteriorly x 1 cm. from side to side. 



Test tough and leathery, very stiff, much corrugated on outer surface (fig. 6). 



Mantle adhering closely to test, yellow, opaque and very muscular. Strong 

 sphincters, and diaphragms at the base of the siphons. 



Branchial Sac with six folds on each side. There are about seven or eight bars on 

 a fold, and three rows of meshes in the interspace. 



There are three sizes of transverse vessel, arranged symmetrically so : tr, tr", tr", 

 tr", tr', 3 tr", tr (fig. 10). The meshes are about square, and contain each four or five 

 very regular stigmata. 



Dorsal Lamina represented by a series of closely placed tentacular languets ; 

 figs. 8 and 9 show two parts of the series. 



Tentacles sparingly branched (fig. 11), and not at all bushy. There are twelve 

 larger ones and a few additional smaller ones interposed irregularly. 



Dorsal Tubercle large and complicated (fig. 12), occupying the whole of the 

 triangular peritubercular area. The opening is anterior, and both horns turn outwards, 

 but in place of coiling are bent abruptly downwards and upwards alternately. 



This little species is a Pyura, according to the nomenclature of Hartmeyer and 

 Michaelsen, and resembles several known forms more or less in appearance. It is, 

 externally, not unlike Pyura (Halocynthia) dura (Heller), with which it also agrees in 

 having six folds on each side of the branchial sac, but they differ totally in the dorsal 

 tubercle, the tentacles, and other internal characters. Another form to which our 

 species shows some resemblance is Halocynthia clavigera (Traustedt) ( = Cynthia 

 nodulosa, v. Drasche), and in this case our irregular dorsal tubercle is not unlike 



