258 Transactions. 



reveals the linear markings, which, though irregular, have one 

 general^direction. The concentric growth-lines are very marked, 

 dividing the entire shell into bands, in each of which the sculp- 

 ture varies somewhat. Prodisoconch and first \ of the shell 

 white, translucent, and devoid of sculpture ; it follows that all 

 young shells are likewise colourless when alive and white when 

 dead. Umbones directed forwards, pointed, shining. Hinge : 

 a large posterior resilium, but no visible external ligament, 

 and no lunule ; 1 cardinal tooth in each valve, sometimes ac- 

 companied by a small point under the umbo in the right valve 

 and § a clumsy thickening of the margin in the left valve, as at 

 fig. 29 ; an anterior and a posterior lateral in each valve ; in 

 some specimens a second posterior in each valve. Pallial line 

 entire. The shell is characterized by two clumsy internal 

 patches of varying shape in different specimens, extending 

 downwards and outwards from behind the hinge ; in young 

 shells these are milky, and may be seen through the shell, remind- 

 ing one of the description of Thyasira albigena, Hedley ; in 

 mature shells these patches spread and thicken clumsily in such 

 a manner as to seriously diminish the capacity of the shell. 



Height, 3*25 mm. ; breadth, 4 mm. ; depth from valve to 

 valve, 2 mm. 



Hab. — Orua Bay, Manukau Harbour ; plentiful in 3 fathoms. 



Type in my collection. 



Rissoina coulthardi, n. sp. Plate XXT, figs. 30-32. 



Shell imperforate, milk-white, loosely coiled, especially the 

 last whorl, the aperture and its posterior callosity occupying 

 exactly one-half the entire length of the shell. Protoconch 

 minute, shining, colourless. Whorls 5, somewhat flat, ex- 

 tremely glossy, the body-whorl with a few longitudinal mark- 

 ings of pale-brown ; in some specimens these stripes are trans- 

 parent. Suture shallow. Base of one specimen (not the type) 

 with 4 spiral lines. Aperture pear-shaped ; a heavy callous 

 at the juncture with the body, and a partly concealed arch in 

 the angle. Columella nearly upright, with a wrinkled twist 

 on the outside of the pillar. Animal and operculum unknown. 



Height, 3 mm. ; width, \\ mm. 



Hab. — Orua Bay, Manukau Harbour ; fifty specimens in 

 3 fathoms. 



Type in my collection. 



Mr. Suter, who has seen this shell, says that it resembles 

 his R. parvilirata. 



Named after the well-known family of Coulthard, in Orua 

 Bay, a member of which kindly assisted me in my dredging. 



