872 PELECYPODA. \_t'ilibnnichia. 



From its nearer ally D. fabale, Hedley, it differs by the straight edge 

 of the anterior margin, and by being smaller and proportionally 

 shorter. (Hedley.) 



2. Dacrydium radians, Suter, 1908. Plate 51, figs. 19. a. 



Dacrydium radians, Suter, T.N.Z.I., xl, 1907 (1908), 355, pi. 27, f. 11. 



Shell small, equivalve, inequilateral, inflated, oblong and very high, 

 semitransparent, thin and fragile, radially finely ribbed. Beaks very 

 small, rounded, directed forwards ; prodissoconch small, broadly 

 ovate, concentrically very finely striated. Anterior end vertical,, 

 straight, dorsally sharply rounded. Posterior end moderately convex, its 

 dorsal margin sloping and straightened ; basal margin acutely convex. 

 Lunular area broadly flattened. Sculpture consisting of numerous 

 fine flatly rounded radial riblets of equal strength and equidistant ; 

 the interstices of the same width as the riblets ; these are crossed by 

 fairly regularly spaced distant concentric sharp ridges. Colour white. 

 Interior slightly nacreous, showing the radial sculpture. Margins 

 minutely crenulate. Posterior hinge-plate narrow, straight, sloping, 

 with numerous small plications, slightly increasing in size as they 

 recede from the resilifer ; the anterior hinge-plate beginning with a 

 small tubercle behind the beak, narrower than the posterior plate, 

 curved, with numerous small plications. Ligament internal, small. 

 Anterior adductor-scar beneath the dorsal margin, oval and high ; 

 posterior scar at the end of the hinge-plate. 



Length, 3-5 mm. ; height, 5-5 mm. ; diameter, 1-6 mm. of the 

 largest valve. 



Type in my collection. 



Hob. Five miles south of Cuvier Island, in 38 fathoms (Captain 

 Bollons). 



SUBORDER 4. PECTIN ACE A. 



Pelecypoda with an open mantle and devoid of an anterior adductor 

 muscle. The gills are folded, and the filaments at the summits and 

 bottoms of the folds are different from the others. The gonads are 

 contained in the visceral mass, and generally open into the kidneys. 

 Foot usually rudimentary, subcylindrical, grooved, and byssiferous. 

 Mantle-lobes free, without siphons, usually with ocelli, papilloe, or 

 other tactile prominences along the margin, and with an inner pro- 

 jecting lamina (curtain) near the margin, at right angles to the plane 

 of the valves. Pallial line simple. 



Shell usually inequivalve, flabelliform, more or less auriculate. and 

 monomyarian ; , shell-structure subnacreous, corrugated, and rarely 

 prismatic, occasionally tubular ; area, when present, amphidetic ; 

 ligament amphidetic, alivincular. 



Animals marine. 



