170 DR. T. DAVIDSON ON RECENT BRACHIOPODA. 



RhynchoneUa, pi. i. fig. 1, 1861 ; E. Sucss, Fossile Mollusken aus Ncu-Sielaiul, Novara Exped. Geol. 

 Theil, Bd. i. Abth. 2, p. 60, pi. xiv. fig. 6, 1864; Dall, Amer. Journ. of Conch, vol. vi. p. 152, 1870 ; 

 Hutton, Catalogue of the Marine Mollusea of New Zealand, 1873, p. 87. 



Hemlthyris mgricans, Dall, Proe. Acad. Nat. Sci. Philadelpliia, 1873, p. 196. 



RhynchoneUa nigricans, T. W. Kirk, List of Marine Mollusea found iu the neiglibourliood of Welling- 

 ton, Transactions New Zealand Institute, vol. xii. p. 303, 1880. 



Shell somewhat tetrahedral, wider than loug. Hinge-line obtusely angular. Dorsal 

 valve convex, divided into three lobes, of wliich the central one forms a broad, slightly 

 raised mesial fold. Ventral valve rather less deep or convex than the dorsal one, with a 

 broad mesial sinus commencing at about a third of the length of the valve and extending 

 to the front; beak pointed and slightly incurved ; foramen longitndiually oval, incom- 

 plete, and situated under the extremity of the beak, margined anteriorly by a small 

 portion of the umbo and laterally by narrow deltidial plates ; beak-ridges tolerably well 

 defined, leaving between them and tlie hinge-line a narrow triangular flattened space. 

 Surface of valves ornamented by a variable nvimber of angular ribs, from twenty to 

 twenty-live on each valve, a few of which are due to interpolation, while from five to six 

 occupy the fold and sinus. Surface of valves crossed by numerous concentric lines, or 

 projecting ridges, of groAvth. Colour bluish or brownish black ; shell-structure fibrous, 

 impunctate. The apophysary system consists of two short curved lamellae. Length 

 11 lines, breadth 13 lines, depth 7 lines. 



Hah. Five miles east of Ruapuke Island, New Zealand ; dredged by Mr. F. J. Evans, 

 R.N., in 19 fathoms, on rock and coral. Abundant at Faveau Strait, and not un- 

 common otr the south Chatham Islands (Hutton). 



Fossil shells referred to this species have been found in New Zealand. 



Ohs. Our first knowledge of this most interesting species is due to G. B. Sowerby, 

 Avho says that, at the time he was describing the shell, only one small young specimen, 

 without indication of locality, was known, wliich was found in the collection of the late 

 G. Humphrey. Since then a number of specimens of all ages have been dredged and may 

 be seen in many collections. In 1882 I I'eceived from New Zealand several examples, and 

 redescribed and figured the species. 



When quite young, and up to a certain age, the shell is triangular and somewhat 

 compressed, and many adult examples are unsymmetrical, from the fold and sinus being 

 moved more to one side than the other. The yoving shells are often found attached in 

 groups to an adult example, or to a sponge or rock. 



The striking resemblance presented to more than one Jurassic or Cretaceous species of 

 RhynchoneUa is very remarkable. Some fossil specimens of 11. nigricans described by Prof. 

 Suess from Kohuron in New Zealand measured 13 lines in length by 14 in breadth. 



97. Rhynchonella nigricans, var. pyxidata, R. B.Watson, MS. (Plate XXIV. fig. 20.) 



RhynchoneUa nigricans, var. jjixydata, Davidson, Report on tlie Bracliiopoda, Voyage of H.M.S. 

 ' Cliallenger,' Zool. vol. i. p. 59, pi. iv. fig. 14, 1880. 



Var. pyxidata. Shell transversely oval, widest anteriorly, tapering posteriorly, wider 

 than long. Dorsal valve uniformly convex to about half its length, where a broad mesial 



