428 Dr. J. Gwyn Jeffreys on 



on eacli side ; it is not so convex tlirou2;liout ; and tlie ribs are 

 twice as many and finer. In shape it somewhat resembles 

 L. ovafa, but is more delicately ribbed, and especially has a 

 central furrow. 



Lima gibla *, Jeffr. 



Differs from L. subovata in being larger and proportionally 

 broader, and in having a somewhat oblique outline ; it is 

 remarkably gibbous, pinched up at the sides, and much more 

 sharply })ointed in front ; and the ribs are much slighter, more 

 irregularly disposed, and sometimes more or less wanting. In 

 every state of growth the two species are distinguishable by 

 these characters, although found together. L. 0*3. B. 0"2. 



Station 9, 1750 fms. ; 12, 1450 fras. ; 16, 1785 fms. Single 

 valves and fragments. 



Mytilidae. 



Idas t, Jeffr. 



Shell ti-ansversely oblong, thin, nacreous : ligament exter- 

 nal : cartilage none : liinge toothless : hinge-plate crenated on 

 both sides of the beaks. 



Perhaps allied to Myrina^ although that genus has an in- 

 ternal ligament or cartilage, and it wants the remarkable cha- 

 racter afforded by the hinge-plate being crenated. Modiolaria 

 and Crenella, as well as Dacrydium, have the hinge-plate 

 crenated on the posterior side; but the sculpture in these 

 first named two genera is very different from that of Idas^ 

 and Dacrydium has an internal cartilage. Idas resembles 

 Area in shape. 



Idas argenteiis |, Jeffr. 



Shell having the shape of an in-egular parallelogram, of a 

 delicate texture, rather opaque, iridescent : sculpture^ very fine 

 and close-set transverse stria and microscopic longitudinal 

 strise ; the latter radiate from the beaks and cover the whole 

 surface of the shell : colour silvery white, except the beaks 

 which are reddish brown : margins straight at the back and 

 in front, rounded on the anterior and smaller side, and sloping 

 from the back with a curved outline on the posterior side : 

 heahs circular and incurved, placed near the anterior side : 

 ligament not observable, in consequence of the specimens 

 being imperfect and consisting of single valves only ; but it is 



* Gibbous or hunched. 



t One of the Argonauts, the " valorous " (see Morris's ' Life and Death 

 of Jason'). 

 \ Silvery. 



