part 3] THE TEIAS or xew zeala^'D. 229 



Mextzeliopsis, gen. no v. (PI. XXIII, figs. 11-18.) 



Shell thin, the growth-Unes being visible on the inner surface. 

 Beak of the ventral valve prominent, arched, and tapering rapidly. 

 Hinge-line straight and rather shorter than the greatest width of 

 the shell. Area triangular, concave, striated parallel to the margin, 

 with an open triangular delthyrium. The hinge-teeth situated on 

 each side of the delthyrium are somewhat prominent, and are sup- 

 ported by two sharp plates. A sharp and prominent median septum 

 extends for nearly half the length of the ventral valve. The dorsal 

 valve is flatter than the ventral. Dental sockets are present, and 

 between them is a short, blunt, cardinal process. An obscure 

 cardinal area is present in the dorsal valve, and there is a faint 

 miedian dorsal septum. Muscular and vascular impressions are 

 •obscure. The outer surface of both valves bears prominent, fairly- 

 equidistant, more or less foliaceous growth-lamellse, and is covered 

 with tubular spines measuring up to 3 or 4 mm. in length. The 

 spines generally occur on the surface between the growth-lamellse, 

 but occasionally the latter are prolonged into spines. There is a 

 more or less prominent dorsal median fold and ventral sinus, -and 

 fainter lateral ridges. Owing to the feeble articulation the valves 

 are generally found separated. 



A specimen which I ground down showed the spiralia directly 

 •connected wdth the crui-al processes, and two discrete jugal processes, 

 a, condition which obtains in the true Spirifers and in Meiitzelia. 



The following points show that the brachiopod is reallj^ a thin- 

 :shelled spiny Mentzelia : — 



(a) The outline, area, and sulcation are that of Mentzelia. 



(b) There is a strong ventral median septum with sharp dental plates on 



each side of it, well seen in every cast of the ventral beak. 



(c) The only specimen that I had available to grind down showed that the 



junction of spirals and crura was simple, and the jug-a apparently 

 discrete. 



(d) The shell- structure is fibrous and silky, but on the only specimen that 



I have which shows any of the test no pimctation could be seen ; 

 if present, it is very faint. 



The founding of a new genus or subgenus for this shell requires 

 some explanation. Mentzelia is generally a perfectly-smooth 

 shell, but Bittner mentions the fact that von Schauroth found a 

 -specimen of Mentzelia mentzeli in the German Muschelkalk with 

 a covering of hair-like spines. The New Zealand form, at least 

 two species of wdiich seem to occur, has the surface of both valves 

 •covered w^th comparatively long tubular spines. It bears a similar 

 relation to Mentzelia as Acantliotliyris does to Bliynclionella. 

 I adopt the commoner species M. sjrinosa as the genotype. 



Locality and horizon. — It seems to be confined to the 

 Kaihiku Beds, Ladino-Carnic. ^I'he only true Mentzelice that I 

 found in New Zealand were in the Rhaetic. On looking over the 

 material that I collected at Mount Heslington, in the Nelson 

 ■district, I find some dorsal valves of ,a small spiny brachiopod, 



Q. J. G. S. No. 291. ^ T 



