Mesodesma.] PELECYPODA. 959 



2. Mesodesma ventricosum, Gray, 1843. Plate 59, fig. 18. 



Mesodesma ventricosa, Gray, Dieff. N.Z., 1843, 252 ; C.M.M., 68 ; Crit. List, 

 43 ; Ereb. & Ter., 5, pi. 3, f. 6 ; Hutton, J. de Conch., xxvi, 48 ; M.N.Z.M., 

 145. Paphia ventricosa, Gray : Hutton, P.L.S. N.S.W., ix, 519. Meso- 

 desma elongata, Quoy and Gaimard : Hutton, C.M.M., 68 ; not of Quoy 

 and Gaimard. 



Shell large and solid, ovate, wedge-shaped, inequilateral, truncated 

 behind, ventricose, white or fulvous. Beaks slightly raised, approxi- 

 mate, directed slightly backwards. Anterior end much longer than 

 the posterior, regularly rounded, the posterior margin long and 

 straight, very slowly descending ; posterior end short, truncated, and 

 narrowly convex towards the basal margin, the dorsal slope steep, 

 nearly straight ; basal margin slightly rounded, ascending posteriorly. 

 Escutcheon broad and long, flattish, bordered on each side by 2 ribs 

 descending from the beaks towards the truncation of the posterior 

 end. Sculpture consisting of fine, dense, somewhat irregular concentric 

 strise, more prominent at the ends, and very faint radiate striae, more 

 distinct on the anterior part of the valves. Epidermis thin, horn- 

 coloured, pellucid, extending beyond the margins. Colour usually 

 dirty-white, sometimes light fulvous. Interior white, porcellanous. 

 shining, with numerous rather distant radial rays. Margins simple, 

 thin and sharp. Hinge : Right valve with a very slender sharp 

 cardinal at the front of the resilifer, and 2 anterior and 2 posterior 

 lateral teeth, the former longer than the latter ; left valve with a 

 stout, compressed, oblique cardinal, and 1 anterior and 1 posterior 

 lateral tooth, both of about the same length and strength. Resilifer 

 narrowly triangular, extending far downward, the resilium very 

 strong, pyriform in cross-section. Ligament amphidetic, short, the 

 posterior part thicker and connected with the resilium. Adductor- 

 scars subequal, pyriform, the anterior deeper and surrounded by a 

 prominent callosity on the posterior side. Pallial line far removed 

 from the margins, especially on the anterior end ; pallial sinus hori- 

 zontal, not quite reaching to the middle of the disc, extending above 

 from the lower margin of the posterior scar, its anterior end semi- 

 circular. 



Length, 112 mm. ; height, 70 mm. ; diameter, 37 mm. 

 Type in the British Museum. 



Hob. North and South Islands, in sand between tide- 

 marks ; more common on the northern shores, especially on the west 

 coast. 



Remarks. The animal of this species is considered a great delicacy 

 by many people, and is sometimes exhibited for sale in Auckland 

 fish-shops. 



Maori. Tairaki (teste Captain Bollons). In the North generally 

 known under the name toheroa. 



