1076 APPENDIX. 



farther the lamella? become reflected and united. Colour pale or 

 deep red, sometimes colourless. (Davidson.) 



Length, 27-5 mm. ; breadth, 25' 4 mm. ; depth, 14-8 mm. 



Hob. Common. Chatham and Auckland Islands. 



Fossil in the Pliocene. 



Fam. RHYNCHONELLID^E. 



Genus 1. HEMITHYRIS, d'Orbigny, 1847. 



1. Hemithyris nigricans, Sowerby, 1846. 



Bhynchonella nigricans, Sow., P.Z.S., 1846, 91 ; Thes. Conch., i, 1846, 342, 

 pi. 71, f. 81, 82 ; Hutton, M.N.Z.M., 178 ; Davidson, Trans. Linn, Soc., 

 iv, pt. ii, 1887, 169, pi. 24, f. 16-19 Hemithyris nigricans, Sow. : 

 Call, Proc. Acad. Nat. Sci. Philadelphia, 1873, 196. 



Shell somewhat tetrahedral, wider than long. Hinge-line obtusely 

 angular. Dorsal valve convex, divided into 3 lobes, of which the 

 centra] 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 longitudinally oval, incomplete, 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 tole- 

 rably well denned, leaving between them and the hinge-line a narrow 

 triangular flattened space. Surface of valves ornamented by a vari- 

 able number of angular ribs, from 20 to 25 on each valve, a few of 

 which are due to interpolation, while from 5 to 6 occupy the fold and 

 sinus. Surface of valves crossed by numerous concentric lines, or 

 projecting ridges, of growth. Colour bluish or brownish black ; shell- 

 structure fibrous, impunctate. The apophysarij system consists of 2 

 short curved lamellae. (Davidson.) 



Length, 23-3 mm. ; breadth, 27-5 mm. ; depth, 14-8 mm. 



Hob. Five miles east of Ruapuke Island, in 19 fathoms, on rock 

 and coral (E. J. Evans, R.N.). From Great Barrier Island to Stewart 

 Island, but more common in the South. Chatham Islands. 



Fossil in the Miocene and Pliocene. 



