KNOWN SPECIES OF MARINE OSTRACODA. 377 
ages ; and, so far as I have been able to ascertain, the following changes may generally 
be observed in tracing upwards a series of specimens from the youngest to the fully 
_ formed adult. 
In the young state the valves are very fragile, pellucid, smooth, and much elongated ; 
the anterior margin is produced into a wide, projecting, flattened border, and the pos- 
terior margin is likewise considerably produced at its inferior angle: the three tubercles 
on the lateral aspect of the valves are very large and conspicuous. This state, which 
I propose to call var. nuda, is represented in Pl. LIX. figs. 9 & 10. In a further 
advanced stage of growth the surface-markings (pittings or reticulations) become 
apparent, the tubercles more fused together and less prominent, and there is a wide, 
flattened, marginal border nearly or quite round the shell. At the same time the 
general outline is more rounded, and the terminal teeth begin to appear. In this stage 
it is referable to C. latimarginata, Speyer (Pl. LX. fig. 13, a—c). In the mature state 
the teeth are more numerous; the flattened marginal belt is, in great measure, lost ; the 
reticulations or pittings are well developed, and the tubercular eminences less con- 
spicuous. This stage of growth coincides with C. lyrata, Reuss, and is shown in Pl. LIX. 
fig. 12,a-c. In extremely old specimens the surface-markings become almost obsolete, 
being either worn away by attrition or perhaps obliterated by constant deposit of new 
shell in the interstices of the sculpture. ‘he difficulty of investigating these closely 
related forms has been considerably increased by the mutilated condition of most of the 
specimens. It is seldom that I have been able to meet with perfect shells, the valves 
being almost always separated. On this account the figures of the dorsal and ventral 
aspects of the different varieties are not so complete as I could have wished. My 
observations of their development have been made, therefore, to a considerable extent 
on an undescribed British species (C. mutabilis, Brady, MS.) which is nearly allied to the 
present. Several stages of the growth of this form are figured in Pl. LIX. fig. 14, a—h. 
The varieties there shown (which, it can scarcely be doubted, are dependent chiefly upon 
stages of growth, but partly also upon habitat) have their precise counterparts amongst 
the Norwegian and Arctic specimens, also figured in Pl. LIX. 
13. CyTHERE LACTEA, n.sp. (Pl. LX. fig. 3, a-c). 
Carapace quadrangular, convex. Extremities nearly equal; anterior rounded, pos- 
terior flattened and produced along its lower half. Dorsal and ventral margins 
nearly straight, slightly sinuate. The lateral aspect of the valves exhibits a very large 
rounded tubercle, connected with a posterior transverse ridge by a longitudinal emi- 
nence. A flattened belt runs round the anterior margin, and is crossed at intervals by 
short ridges. Dorsal profile angular, oval, very broad. Surface of the shell closely 
reticulated. 
Length gg in. (‘63 mm.). 
Hab. Australia (17 fathoms, in sand), One specimen. 
VOL. V.—PART V. 3D 
