242 Transactions. — Zoology. 



Fam. SPHiERIIDiE. 



Cardinal teeth not exceeding two in each valve, and ex- 

 hibiting a cessation of development at an early stage. (Dall.) 



The New Zealand species of Sphcerium and Corneocyclas are 

 not easily separated with regard to their generic position, as both 

 are about to the same extent inequilateral, though in Corneocyclas 

 the anterior part is mostly more attenuated and the nepionic 

 shell sometimes more conspicuous than in Sphcerium. The car- 

 dinal teeth are very variable, and it is a tedious job to ascertain 

 the genus from these alone, but they assist in the general diag- 

 nosis. To be absolutely certain living specimens should fcbe 

 examined, Sph&rium having two siphonal tubes, Corneocyclas 

 only one ; but with the specimens to be described that was 

 out of the question. Fortunately I have specimens of both 

 genera from New Zealand in my collection, which I examined 

 when alive, and these were of great help to me for the study 

 of the various specimens collected by Messrs. Lucas and 

 Hodgkin. 



Much useful information was obtained from the chapter on 

 the family Sph&riidai in the classical work of Dr. W. H. Dall, 

 " Tertiary Fauna of Florida." 



The indices I calculated for the Sphosriida; are part of those 

 used for the Unionida? : iii. = index of height ; vii. = index of 

 diameter ; x. = umbonal index. 



Genus Sph^rium, Scopoli (1777). 

 Subgenus Sphjerium, Scopoli, s.s. 



Type : S. corneum, Linne. 



The nepionic shell passing into the adult without any distinct 

 demarcation ; the anterior end shorter ; the ligament subs- 

 ternal ; the two right cardinals widely divergent and coalescent 

 at their adjacent or upper ends, thus apparently forming but one 

 tooth, but which if it had continued in development would have 

 separated into two ; the widening of the ventral angle causes 

 the A -shape to disappear ; the nepionic shell (and consequently 

 the beaks) is finely concentrically striate or even nearly smooth 

 and rather convex. (Dall.) 



Sphaerium novae-zelandiae, Deshayes (1853). 



Cat. Conchif. Brit, Museum, p. 272 ; P.Z.S., 1854, p. 342. 



(1.) Lake Rotoiti (Stat. 15 — From muddy bottom and weeds 

 in 6 ft.). — Three specimens of nearly equal size, suborbicular, 

 subequilateral ; colour grey, near the ventral margin yellowish ; 

 beaks covered with a ferrugineous incrustation. Nepionic shell 



