972 PELEC'YPODA. [EulameUibranchia. 



part of the pallia! sinus and the other to the anterior lower side of 

 the posterior adductor. Margins smooth, thin and sharp. Hinge : 

 Right valve with 2 cardinals of equal length, united above, A- shaped, 

 and 2 posterior lateral laminae, the upper obsolete ; left valve with a 

 high A-shaped cardinal, both arms of which are of equal length, a 

 low sharp accessory lamella behind it, 1 high triangular lateral tooth 

 in front, and a rather long, thin, and slightly raised posterior 

 lamella ; resilifer very oblique, triangular. Ligament rather short, 

 thin, the greater part of it internal. Adductor - scars subequal. 

 the anterior oval, deep, with 2 oblong pedal retractor scars behind it, 

 the posterior scar shallow, irregularly rounded. Pallial sinus deep 

 and high, extending to beyond the middle of the valve, anteriorly 

 narrowly convex. 



Length, 47mm.; height. 18mm.; diameter, 8-5 mm. (type). 

 Length, 94 mm. ; height, 45 mm. ; diameter, 15 mm. (large specimen). 



Animal (Dall, P. Mai. S., iii, 86). Siphons naked, and com- 

 pletely united, the opening surrounded by conspicuous papillae ; 

 mantle-edges smooth, united in front and forward on the ventral 

 margin ; foot quadrate, compressed, smooth ; labial palpi long and 

 large, their free ends extending behind the foot ; the ctenidia are 

 symmetrical, coarsely plicate, and extend forward, diminishing in 

 size, a considerable distance between the palpi. 



Type in the Mus. Hist. Nat.. Paris. 



Hab. North and South Islands, from below low-water mark to 

 about 30 fathoms ^ in some places, like New Brighton, it is evidentlv 

 common in a depth of from 3 to 5 fathoms. 



Remarks. In Trans. Wagn. Free Inst., iii, pt. 4. 888, Dr. W. H. 

 Dall says that the type, Z. acinaces, differs from Z. Dcshayesi by 

 the total absence of lateral teeth. This is not correct, for Quoy and 

 Gaimard say, " En avant de la dent cardinale gauche en est une 

 laterale bien marquee, fort raprochee et triangulaire." This part is, 

 unfortunately, left out in the translation of the diagnosis given bv 

 Hut ton. I have examined many specimens, and always found this 

 anterior lateral, and mostly also the posterior lateral lamina, to be 

 present. 



The material from various localities, as represented in my col- 

 lection, leads me to the conclusion that the typical form is from 

 deeper water, about 10 to 30 fathoms ; Z. Deshaye.si and Z. solenoides 

 are large forms living in lesser depth, from below low-water mark to 

 about 5 or 10 fathoms, and Z. Cumingiana is a half-grown form of 

 the latter, being found associated with the large shells. All the small 

 specimens from deep water have the dorsal margin more or less 

 excavated ; but between these and the large forms all intermediate 

 grades are found. 



Maori.- Peraro (teste Captain Bollons). 



Fossil in the Miocene and Pliocene. 



