Diploduti.] PELECYPODA. 945 



very thick on the anterior lower part of the valves ; the callosity 

 below the pseudo-cardinals transversely finely wave-striated ; an 

 oblique straight ridge runs from the umbonal cavity to the lower 

 part of the posterior adductor-scar. Hinge : Right valve with 2 

 compressed, crenated pseudo-cardinals, the anterior tooth smaller, 

 and 1 long, substraight, posteriorly raised and finely corrugated lateral 

 tooth ; left valve with 2 crenated subequal pseudo-cardinals, and 2 

 long laterals, the upper one shorter and smaller than the lower. 

 Ligament long, strong. Adductor-scars : There are 2 in front, a deep 

 roundish one with a straight upper edge below the pseudo-cardinals, 

 and a faintly impressed small one behind it ; posterior scar not im- 

 pressed, large, oval. Pallial line simple, very distinct, the basal 

 margin much thickened outside it on the anterior two-thirds. 



Length, 50 mm. ; ratio of length, height, and diameter, 100, 52, 

 32 respectively. An average form selected from about 100 specimens 

 shows the following dimensions : Length, 86 mm. ; height, 48 mm. ; 

 diameter, 25 mm. 



This shell has twenty-two rest-marks. 



Type in the K.K. Hofmuseum, Vienna. 



Hob. New Zealand (" Novara ' Exped.) ; River Wairarapa 

 (Captain Hutton) ; near Napier (Colenso), two specimens in the" 

 Dominion Museum ; Papuni district, between Maungapohatu and 

 Poverty Bay (Elsdon Best) : Albury Creek and Ashburton River 

 (W. W. Smith). 



Remarks. In Bunker's diagnosis the shell is said to be " tenui- 

 cula," but it is the most solid New Zealand species. Dunker mentions 

 that it has some analogies with Unio pictorum, L., a common European 

 shell, which is decidedly a species with thick valves. 



SUBORDER 3. TELLINACEA. 



Eulamellibranchia in which the mantle is not extensively closed, 

 with 2 pallial sutures and 2 well-developed siphons ; the gills smooth. 

 The foot is compressed and elongated. The labial palps very large. 

 Dimyarian. Shell with the pallial line sinuate ; ligament external, 

 seated on nymphs ; hinge normally with an anterior and posterior 

 lateral in each valve ; 2 radial cardinals, of which the anterior is 

 commonly bifid and somewhat pedunculated, and the posterior, as 

 well as the laterals, often obsolete. 



Fam. TELLINID^B, Deshayes. 



Animal having the mantle widely open in front, the edges papil- 

 late ; foot large, laterally compressed, with a byssogenous posterior 

 apparatus, but not byssiferous ; the siphons separate and elongated ; 

 palps very large, triangular ; gills united behind, the external branchial 

 plate directed upwards. 



