34 THE VOYAGE OF H.M.S. CHALLENGER 



thus described in his MS. : " Testa JEuplaciphorce petholatce forma, colore et indole simil- 

 lima ; sed ar. lat. minus definitis ; sculptura, nisi punctulis undique creberrimis, nulla ; etc. 

 Habitat. — Australia, Mus. Cum., No. 67 ; var. 66 also from Australia." 



The four specimens collected by the Expedition are greatly corroded, and were over- 

 grown with Nullipore ; on the removal of the latter what little remains of the original 

 surface of the shell is exposed. 



Shell. — Smooth, simply marked with lines of growth, flat sides meeting at a variable 

 angle. 



Anterior valve. — Small, surface smooth. Under surface with eight slits, teeth fairly 

 long, smooth and sharp ; eaves short. 



Intermediate valves. — Central area: smooth, flat. Lateral areas : inconspicuous, with 

 two or three very faint radiating ridges. Under surface : with a median horizontal rib- 

 like swelling ; sutural laminae broad, but not deep ; jugal sinus wide and shallow ; one 

 lateral slit ; eaves short. 



Posterior valve. — Very small and flat, greatly corroded ; umbo apparently flat and 

 terminal ; posterior border thickened. Under surface : sutural laminae as in intermediate 

 valves, but the jugal sinus is comparatively narrow and deep ; slits and teeth absent ; 

 posterior border much swollen. 



Girdle. — Very thick and fleshy, upper surface having a spongy appearance, owing to 

 being beset with very short horny spines, which are scarcely raised above the surface ; 

 there are tufts of longer spines, three to nine in each tuft, opposite the sutures of the 

 valves ; these have no definite position round the anterior valve. Situated outside these are 

 numerous scattered similar tufts, usually somewhat smaller in size, which pass into an 

 imperfect peripheral fringe of spines (see PI. III. figs. 13, 13a). 



Colour. — All the valves of a uniform dark brown, with a pale (lilac) narrow triangular 

 band along the jugum of the intermediate valves (and anterior area of the posterior valve). 

 Under surface of all the valves of a bluish green colour ; laminae of insertion paler. 



Girdle. — Upper surface dark brown ; under surface dusky orange. 



Size.— Length, 40 mm. ; breadth, 25 mm. ; height, 10 mm.; angle, 125° to 135° (two 

 specimens from 100 to 150 fathoms). Length, 25 to 35 mm. ; breadth, 14 to 17 mm. ; 

 height, 8 to 9 mm. ; angle, 90° to 110° (two shore specimens). 



Plaxiphora carpenteri, n. sp. (PL I. fig. 8, PI. III. figs. 8a-8g). 

 Habitat. — Tristan da Cunha. 



Shell. — Smooth, the sides meeting at an angle of 105°. 



Anterior valve. — "With eight radiating ridges, not counting the swollen posterior 

 borders. Numerous concentric minor ridges cause these ridges to be rugose. Under 

 surface with nine slits, two being very close together ; eaves short. 



