66 THE VOYAGE OF H.M.S. CHALLENGEK. 



[PI. XII. fig. 6, a-f. a Shell of female seen from left side, h from above, c 

 from below, c? from front, e male seen from left side, /from below. All magnified 60 

 diameters.] 



7. Oythere demissa, G. S. Brady (PI. XII. fig. 1, a-j). 



Cythere demissa, Brady, Ann. and Mag. Nat. Hist., 1868, ser. 4, voL ii p. 180, pi. xii. figs. 1, 2. 



Shell seen laterally, oblong, subovate or subreniform, not much higher in front than 

 behind, height equal to about half the length ; anterior extremity somewhat obliquely 

 rounded, posterior only poorly rounded, subtruncate ; dorsal margin highest in front of 

 the middle, where it is slightly gibbous, thence sloping steeply to the front, and with a 

 slight curve backwards ; ventral margin sinuated in the middle ; seen from above, the 

 outline is ovate, with wide, obtuse, or subtruncate extremities, and nearly parallel sides, 

 width considerably less than half the length, the whole posterior extremity and the 

 hinder parts of the lateral margins present a succession of deep notches or crenations, 

 and the anterior extremity is either abruptly truncated or rounded, and broken into 

 tooth-like crentations ; end view subcircular, with a tendency to hexagonal form. Shell- 

 surface thickly beset with subrotund or angular excavations, which, on the ventral 

 surface, coalesce so as to form well-marked grooves and ridges. Length, 1-5 8th of an 

 inch ('43 mm.). 



Several specimens, varying a good deal in minor details, but agreeing in general 

 character, and, I think, all belonging really to one species, which may fairly be identified 

 with Cythere demissa, were found in a dredging made at Port Jackson, in a depth of 

 2 to 10 fathoms (Station 163). The most distinct of these forms are represented in 

 PL XII., fig. 1, e and/, being probably the male. The tapering and strongly sculptured 

 form shown in figures g-j, may perhaps be looked upon as the fully-developed adult 

 female, of which figures a-d show an earlier stage. 



[PL XII. fig. 1, a-j. a Shell of female seen from left side, h from above, c from below, 

 d from front, e male seen from left side, /from above, g adult female seen from left side, 

 h from nljove, i from below, ^ from front. AH magnified 80 diameters.] 



8. Cythere ovalis, n. sp. (PL XIV. fig. 4, a-d). 



Shell oblong, rather tumid ; seen from the side, elongated, subreniform, height equal 

 to about half the length, and nearly the same throughout ; extremities well rounded ; 

 the anterior fringed with a regular series of small teeth, about twelve in number, 

 posterior having a smaller number of similar teeth at the longer angle ; dorsal margin 

 very slightly arched, sloping gently from before backwards, ventral nearly straight ; seen 

 from above, the outline is regularly ovate, widest behind the middle; extremities 

 subacuminate, sides gently curved, converging gradually towards the front, and more 

 suddenly towards the hinder end, width equal to the height; end view subcircular. 



