Verticordia. \ PELECYPODA. 1035 



1. Verticordia setosa, Hedlev, 1907. Plate 54, figs. 15, a. 



Verticordia rhomboidea, Hedley, T.N.Z.I., xxxviii, 1905 (1906), 72, pi. 2, 

 f. 12-14 ; not of Tate, 1887. V. setosa, Hedley, Rec. A.M., vi, 1907, 303. 



Shell small, inflated, subrhomboidal, inequilateral, right valve 

 slightly clasping over the left along the dorsal margin, substance 

 very brittle, easily flaking off. Umbones incurved, rather distant, 

 usually eroded. Anterior end descending abruptly from the umbones, 

 angled below towards the horizontal ventral margin ; posterior end 

 flatly rounded, the dorsal margin long, convex, very little oblique. 

 Lunule slightly excavated ; dorsal area defined by the radial ribs. 

 Sculpture : No incremental growth-lines, about 22 prominent sharp 

 radial ribs which strongly denticulate the margin and imprint the 

 nacreous interior ; the surface has everywhere close-set grains which 

 develop minute sharp prickles. Hinge : Right valve with a large 

 conical tooth under the lunule, and a posterior lateral beneath the 

 dorsal area ; left valve with a minute tooth under the umbo and no 

 lateral ; ossicle not found. 



Length, 5-75 mm. ; height, 5 mm. (type). 



Type in the Dominion Museum. Wellington. 



Hob. Off. Great Barrier Island, in 110 fathoms (type) ; near 

 Cuvier Island, in 37 fathoms (Captain Bollons). 



ORDER 4. SEPTIBRANOHIA. 



The Septibranchia are dimyarian Pelecypods in which the mantle 

 remains fairly open and has 2 sutures and 2 siphons. The foot is 

 long and slender ; the byssus rudimentary or absent. The pallial 

 line is simple or very slightly sinuous. The essential character of the 

 group is the disappearance of the gills as respiratory organs, a character 

 which is not found in any other Pelecypod. The gills are trans- 

 formed into a muscular septum which extends from the anterior 

 adductor muscle to the point of separation of the 2 siphons, and 

 surrounds and is continuous with the foot. The septum, therefore, 

 has exactly the situation and the relations of the branchial septum of 

 the majority of the Pelecypoda, which divides the pallial cavity into 

 2 chambers. The muscular septum is inserted on the shell, especially 

 in the neighbourhood of the 2 adductor muscles ; it is pierced by 

 paired orifices, which admit the passage, of the water. 



The Septibranchia are all marine, inhabit considerable depths of 

 the sea, and are carnivorous. 



Fam. CUSPIDARIID^S, Ball. 



Animal having the siphons long 'and united, their extremities 

 surrounded by tentacles ; foot narrow, with a rudimentary byssus ; 

 palps greatly reduced or absent ; branchial septum pierced by 4 or 5 

 pairs of very narrow symmetrical orifices. The sexes are separate. 



