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



setose cilia." At my request, Dr Halifax of Biightou. made for me a series of prepara- 

 tions of th.e mantle of both Discina Icevis and Discina ailantica. These last, from specimens 

 brought home by the Challenger Expedition, showed in the most admirable manner the 

 highly vascular mantle, fringed with long horny setse entirely agreeing with the descrip- 

 tion and illustrations of Professor Owen and Dr S. P. Woodward. The cirri are of great 

 length, and barbed throughout, with spine-like asperities, in some cases they bifurcate 

 near their extremities, and lie close together at their origin. In some specimens of 

 Discina Icevis, great numbers of full-grown PedicelUnce, belonging to the Polyzoa, adhered 

 to the long barbed cu-ri (PL IV., fig. 17, b), looking like Lingulae, with their long pliant 

 peduncles. The smaller valve of Discina atlantica was described by Dr Gwyn Jeffreys, 

 from a North Atlantic specimen, obtained during the "Valorous" Expedition — "Flat, thin, 

 having near the middle a comparatively small round disk, within which is an oval slit for 

 the passage of the byssal stalk (peduncle) of attachment. This disk is slightly sunk within 

 a calcareous substance to which it is attached, as if the byssus had the power of excava- 

 tion ; the rest of the lower valve is free and concentrically striated, like the upper valve. 

 Muscular (adductor) scars in the upper valve, club-shaped, rather close together, no scars 

 observable in the lower valve, not the slightest trace of tubular or perforated structure 

 could be detected in either valve, with one of Smith's and Beck's best microscopes, under 

 a lens of one-fifth power." I am not certain that this species has been hitherto positively 

 found in the fossU state, but Dr Gwyn Jeffreys thinks that the Discina fallax, S. Wood, 

 from the crag of England, may, perhaps, be referable to the species under description. 



Discina stella, Gould (PI. IV. fig. 19, a). 



Discina stella, Gould, Mem. Boston Soc. Nat. Hist., vol. vii. p. 323; Otia Conch., p. 120, 1860. 



Orbicula stella, Reeve, ConcL Icon., pi. i. fig. 1, 1862. 



Discina stella, DaU., Am. Journ. of Conch., vol. vii. part 2, p. 76, 1871. 



Shell orbicular, about as broad as long ; upper valve conical, and moderately elevated, 

 vertex sub-central, surface marked by numerous radiating stri^, vertex almost smooth, 

 yellow. Attached valve almost flat. Length 6, breadth 6, depth 3 mm. 



Habitat. — Five upper valves of this species were dredged by the Challenger Expedi- 

 tion, off Bermuda, at Station 190, lat. 8° 56' S., long. 136° 5' N., on September 12, 1874, 

 in 49 fathoms. Bottom temperature, 23*°9 C. Sea bottom, mud. It has also been found 

 by Mr Cuming, near Singapore, and the Philippine Islands. Stimpsom and Wilkes c[uote 

 it from the China Seas. 



Observations. — In his Conch. Icon., Reeve states that " this species has a wide distri- 

 bution in eastern seas. On comparing authentic specimens received from Dr Gould, of 

 which is given at fig. 1, b, collected in the China Sea, by Wilkes' exploring expedition, I 

 find them identical with specimens collected l^y Mr Cuming, attached to fragments of 



