"202 DE. C. T. TEECHMANjSr Olf [vol. Ixxiii, 



described, occurs. The bed is specially well seen at Nugget Point, 

 where it is about 10 feet thick. 



Ee marks. — The specific name that Zittel gave to this shell 

 seems to imply some doubt as to its real affinities. I never found 

 the two valves together, but the New Zealand Geological Surve}^ 

 ■Collection includes one or two examples in this condition, though 

 not well enough preserved to show whether it is an exactl}' equivalve 

 shell or not. This, as also the absence of muscle-scar impres- 

 ;sions, makes a certain attribution impossible at present, but I 

 :strongly sus]Dect that the form here described may be related to 

 tihe Myalinidse rather than to Ifi/tilus. 



Mytilus (P) mieabilis, sp. nov. (PI. XX, figs. 9« & 9 5.) 



Shell inflated, very strongly arched ; the valves are nearly twice 

 .as deep as they are long, very much compressed antero-posteriorly. 

 Beak small, anteriorly situated or terminal ; area very short Avith 

 a ligament-groove behind it, bearing faint parallel striae. There is 

 a small apical septum in the interior of the beak. In one specimen 

 I detected a posterior muscle-scar of fair size, but saw no trace of 

 .an anterior scar. The hinge is edentulous. 



Length=o2 mm. ; height = 108 mm. ; depth of valve = 100 mm. 



Locality and horizon. — It occurs rather commonly in the 

 3Iyfilus-prohlemaficus Bed at Eighty-Eight Valley, south of the 

 Wairoa (xorge. Nelson. Carnic. 



Remarks. — This shell has been called GnjplicEa in New Zealand 

 ■Greological Survey reports. The valves are always separated, but 

 I have no doubt that it is an approximately or completely equi valve 

 shell, as I collected both left and right valves. I feel sure also, 

 after examining the shell-structure, which is of a laminar nature, 

 that it is related to Mijtilus prohlematicus, with which it occurs in 

 intimate association and with which it seems to be connected by a 

 series of intermediate forms that may be young specimens. It 

 suggests, in fact, an enormously overgrown specimen of J\Tyfihis 

 jprohlematicus in which the A'alves have become strongly arched. 

 Fully-grown examples with the two valves together must have 

 presented an extraordinary a])pearance, quite unlike that generally 

 associated with Mijtilus. a fact Avhich causes me to question the 

 generic attribution both of this and of Mytilus prohlemaficus. 

 The holotvpe is a right valve in my collection. The New Zealand 

 Geological Survey possesses several specimens from Eio'hty-Eight 

 Valley. This form generally occurs in a poor state of preserva- 

 tion, with the shell more or less completely dissolved away. 



HoKO^'UIA, gen. nov. (PI. XX, figs. 4-5 h ; PI. XXII, figs. 1-5.) 



The shells belonging to this genus show verj^ considerable 

 diversity in size, shape, degree of inflation, thickness of shell, and 

 situation of the beak. Some recall Lima in general shape, others 

 JSLjalina or Avicula. 



The shell-structure is more or less platy and foliaceous, recalling 



