64 
have a varying structure as to the genera; they are of the eulamelli- 
branchiate type and are fused to each other and to the mantie at 
the anal slit. The intestine runs directly, in a slight curve back- 
wards from the stomach, from which it issues on the right side. 
Concerning the hinge, a great variation also prevails. The teeth 
may be completely reduced, or they are present in a vestigial shape 
only, or finally, they are well-developed. The hinge seems to re¬ 
present the cyrenoid type as well as the lucinoid one of Ber¬ 
nard; thus in G. faba and trapezina we find the latter, as well as 
in Kidderia bicolor and in G. smithi (which may be a Kidderia ; cf. 
Hedley 1916, pi. II, figs. 17—19), and in Neogaimardia the former. 
The ligament is external or subinternal in Gaimardia, subinternal 
in Kidderia and distinctly internal in the new genus Neogaimardia. 
To this family I refer the genus Gaimardia {=Modiolarca; for 
the change of name cf. I red ale 1915) and the closely related 
Kidderia Dall 1876, as well as the new Neogaimardia (type Kellia 
rostellata Ta te). The interrelation of these genera which are all 
represented in the New Zealand fauna, is shown in the following 
scheme: 
I. Animal with 2 giil plates on each side. 
A. Giils with well-developed interlamellary septa extending 
nearly all along the height of the lamellae; plates folded be- 
tween them; foot with mucus pore separated from byssus fur- 
row; ventral mantie suture shorter than the branchial opening. 
Shell rhomboid, with anterior rostrum; hinge of the lucinoid 
type with indistinct teeth; ligament subinternal or external 
Gaimardia Gould 1852. 
Type: G. trapezina (Lamarck). 
B. Gilis with incomplete interlamellary septa (present in the 
marginal part only, about 1/3 of the height), plates simple, smooth; 
foot with mucus pore debouching in the front end of byssus 
furrow; ventral mantie suture longer than both siphonal slits 
together. Shell elongate, rostrum indistinct 
Kidderia Dall 1876. 
Type: K. minuta Dall. 
II. Animal with 1 giil plate on each side (= the inner or an¬ 
terior one of the preceding group); no interlamellary connec- 
