part 3] 



THE TEXAS OF NEW ZEALAND. 



233: 



Sipirigera eurycolpos Bittner,^ of the Alpine Dachsteinkalk, also 

 belongs to this group, but differs from the present form in shell- 

 outline and other details. The internal structure is essentially 

 similar to that of Sp. oxycolpos, which Zugmayer has described ini 

 detail, a structure which exists in a more exaggerated form in 

 the group next to be described. 



I have very strong reasons to think that the New Zealand Trias, 

 if thoroughly searched, would 3deld more and different forms of 

 the group of Spiriqerce, to which 8p. lureyi, Sp. kaihi/tuana, and 

 Sp. manzavinioides belong. The New Zealand Geological Survey 

 possesses another such form, and I. have fragments of others ; but 

 the rather doubtful localitj^-record of the former, as also the poor 

 condition of my material, makes it unadvisable to found further 

 new species at present. 



Hectoeia, gen. nov. (PI. XXV, figs, la-4ih.) 



The hinge-line slopes very slightly awa}^ from the beaks, and 

 represents the greatest, or nearly the greatest, width of the shell. 



The ventral area extends for 



Fig. 4. — Specimen o/Hectoria sp. nearly the whole length of 



from Carnic shales at Ota- the hinge-line : it is narrow, 



mita, partly ground down. but consjDicuous, and has faint 



parallel striations ; the area 

 ______ --"^ of the dorsal valve is nearly 



obsolete. The ventral beak 

 projects but very slightly 

 above the hinge-line ; the 

 dorsal beak is rather less pro- 

 minent. The valves are almost 

 equally convex ; the ventral 

 sometimes slightly more sa 

 than the dorsal. Both valves- 

 have a more or less pronoun- 

 ced, median, rapidly- widening^ 

 sinus, bounded on each side 

 by rounded lateral folds which 

 diverge from the beak and 

 pass to the anterior margin, 

 where they meet similar folds of the opposite valve. The junc- 

 tion of the valves lies almost in one plane, or is very slightly 

 sinuous. The shell- structure is silky and fibrous, the fibres being 

 mostly directed towards the median line. In a cast that I collected 

 in Carnic beds near Gore, in the Hokonui district, the beak has 

 been pierced by a narrow and long arched tubular foramen, but 

 in others, and especially in the larger and more fully grown 

 specimens, the foramen is filled up and obliterated by the shelly 

 thickening of the beak. The delthyrium is triangular'^and sunken, 

 and in the larger specimens at least is closed. 



1 Bibliography, 4, p. 273 & pi. xxix, %s. 7-13. 



a=Dental sockets. 



6 = Cardinal process of the dorsal valve, 

 c = The recvirving- of the primary lamellae. 

 cZ = The medio-laterally directed spiralia. 



