68 NATURAL SCIENCE. July. 



are not divided up into stigmata, as they are in the case of a typical 

 Simple Ascidian. This peculiar condition of the branchial sac seems 

 to be associated with the abyssal zone, as it has apparently been 

 evolved independently in at least four different groups of deep-sea 

 ascidians, viz., CtUeolus, Fimgulus, Bathyonms, and Pharyngodictyon, while 

 it has not been found in any forms from shallow water. 



In Culeolus the branchial sac is strengthened by the de- 

 velopment in the vessel-walls of a system of gracefully branched 

 and curved calcareous spicules, marked internally by a series of 

 " contour " lines. These are quite different in appearance from the 

 fusiform echinated spicules found in some species of Cynthia. 



Another noteworthy feature in the anatomy of the genus Cnleohis, 

 is the condition of the blood-vessels of the test in some of the species. 

 In C. murrayi the terminal twigs of the vessels open into large vesicles 

 placed just below the surface of the test, and only separated 

 from the external medium by a very delicate membrane. In 

 several of the species there are thin-walled hollow papillae or 

 projections from the surface of the test, and these are in free com- 

 munication with either the large vesicles or the ends of the vessels. 

 This is obviously an accessory respiratory apparatus, permitting the 

 blood circulating in the test (which when the heart contracts dorso- 

 ventrally is impure) to be brought into such close relations with the 

 external water as to ensure a certain amount of oxidation. 



A large number of other new species of Cynthiidae were obtained, 

 but the only others which cannot be referred to a known genus are 

 Bathyoncus mirabilis, B. discoideiis, and B. minutns, forms which agree with 

 the typical Styelinae in having simple tentacles, but differ from them 

 in having a branchial sac of the skeleton type found in Culeolus and 

 Fungidus. Styela is remarkable on account of its very extended 

 bathymetrical range. Most of the species are found in shallow water, 

 some few between tide-marks ; while six species in the collection are 

 from between loo and 600 fathoms, and two, 5. bythia and S. sgitaviosa, 

 both fairly typical members of the genus, were obtained at a depth of 

 2,600 fathoms. (PI. xvi.. Fig. 2.) 



In the Molgulidae, two gigantic pedunculated forms, destitute 

 both of hair-like processes from the test and incrusting sand, have 

 been placed in a new genus, Ascopera. In the Ascidiidae there are three 

 noteworthy new genera — Corynascidia, Ahyssascidia, and Hypohythius, 

 all from deep water. Corynascidia suhmi is, like so many other of the 

 abyssal forms, supported upon a peduncle. The position and course of 

 the intestine are peculiar, and the branchial sac is one of the most 

 beautiful and delicate known. Ahyssascidia is a connecting link 

 between the well-known British genera Ascidia and Corella. It 

 resembles Corella in the position and course of the intestine, while, in 

 the structure of the branchial sac, it exhibits the simpler arrangement 

 found in Ascidia, from which again it differs in the condition of the 

 dorsal lamina, and in the large number of lobes surrounding the. 



