188 F. Chapman and Irene Crespin : 



11. — Tegulokhynchia pyxidata, Davidson, sp. 



Rhynchonella nigricans, var. pyxidata, Davidson, 1880, p. 59, pi, 

 IV., fig. 14. 



Rhynchonella nigricans, var. pyxidata, R. B. Watson (MS.), 

 Davidson, 1887, p. 170, pi. XXIV., fig. 20. 



Hemithyris pyxidata, Davidson, sp. Thomson, 1915, p. 391, foot- 

 note 4. 



Description. — (From Davidson). "Shell transversely oval, widest 

 anteriorly, tapering posteriorly, wider than long. Dorsal valve uni- 

 formly convex to about half its length, where a broad mesial fold, 

 scarcely raised above the general convexity of the valve, occupies 

 the anterior half of the valve. Ventral valve rather less deep and 

 convex than the opposite one, with a broad, well-defined mesial sinus, 

 comencing at a short distance from the extremity of the beak, and ex- 

 tending to the front; beak rather small, acute, and incurved; foramen 

 incomplete, situated under its pointed extremity, laterally margined 

 by narrow deltidial plates; surface of both valves ornamented with 

 about forty to forty-six small, angular, radiating ribs, closely inter- 

 sected by equidistant, squamose, concentric ridges of growth, giving an 

 imbricated appearance to the surface. Colour whitish, sometimes 

 brownish, especally at the beaks." 



" Dimensions. — Length, 9 lines, breadth 10 lines, depth 6 lines." 



Observations. — Davidson states that, " After careful study andl 

 comparison with an extensive series of New Zealand types, I am led 

 to the conclusion that Rhynchonella pyxidata is merely a local variety 

 of R. nigricans." From the present standpoint, after an examination 

 of many other variants of this series, which for convenience are given 

 specific rank, we are inclined to regard T. pyxidata as distinct, on 

 the grounds of having a more incurved beak, a less subtrigonal out- 

 line, whilst the costation is much finer and the ribs are more dis- 

 tinctly burfurcated towards the anterior commissure. Davidson also 

 remarks that T. pyxidata "seems absolutely undistinguishable " from 

 McCoy's " Rhynchonella " coelata from Table Cape. The Table Cape 

 species, however, appears to have a less acute beak, which is not so 

 strongly incurved; the shell is more elongated transversely, and the 

 tegulation is always well developed, whereas in T. pyxidata the growth- 

 lines are is an incipient stage. 



In a communication recently received. Dr. Thomson strongly con- 

 firms our idea of the specific distinction of T. pyxidata. He also 

 points out that the New Zealand squamosa has conjunct deltidial 

 plates, whereas in pyxidata they are discrete. 



Occurrence. — Recent. Dredged by the "Challenger," south of 

 Kerguelen Islands, at a depth of 150 fathoms. 



12. — Tegulorhynchia sublaevis, Thomson, sp. 

 Hemithyris sublaevis, Thomson, 1918, p. 117, see also p. 108. 

 Description. — A small species with a short beak, narrowly and 

 strongly folded, with numerous fine ribs, little imbricated and in many 

 specimens almost obsolete. (From Dr. Thomson's notes.). 



