176 Transactions 



Art. XX. — Notes on New Zealand Mollusca : No. 1, Descriptions of 

 Three New Species of Polyplacophora, and of Damoniella alpha. 



By Miss M. K. Mestayer, Dominion Museum. 



[Read before the Wellington Philosophical Society, 22nd October, 1919 ; received by Editor, 

 21st December, 1920 ; issued separately, 4th July, 1921.] 



Plate XXXVIII. 



In this paper four new species of Mollusca are described, the types of 

 which are in the Dominion Museum, three of them belonging to the order 

 Polyplacophora, or chitons. Two were obtained within a short distance of 

 Wellington, but repeated search has failed to discover further specimens. 

 Damoniella alpha is, unfortunately, the only specimen so far obtained ; it 

 was discovered by Dr. J. A. Thomson in the fossil-beds at Blue Cliffs, 

 Otaio River. It adds a new genus as well as a new species to the New 

 Zealand Tertiary fauna. 



The excellent drawings from which the accompanying plate was prepared 

 were done by Miss J. K. Allan, of Sydney, and hearty thanks are due to 

 her for the careful, accurate work bestowed upon them. 



PLAXIPHOPJDAE. 



Plaxiphora (Maorichiton) Iredale (1).* 

 Plaxiphora (Maorichiton) lyallensis n. sp. (Plate XXXVIII, figs. 7-8.) 



Lyall Bay, Cook Strait, N.Z. 



Shell oval, flatly arched, side slopes straight, surface dull. Anterior 

 valve with eight radial ribs, rendered slightly nodulous by the irregularly 

 spaced growth-lines ; the spaces between the radials appear smooth, but 

 a strong pocket-lens shows traces of V-like sculpture. Median valves 

 squarish, not beaked, nearly smooth ; lateral areas raised, marked off by 

 a strong semi-nodulous rib, the central portion covered with very fine 

 V-like sculpture ; the jugal areas with traces of microscopic striae and 

 pitting ; the pleural areas with a few horizontal wrinkles in a shallow 

 groove anterior to the lateral rib ; this groove is most distinct in valves 4 

 to 6. Posterior valve small, mucro terminal, slightly upturned, pleural 

 areas bounded by a strong marginal rib, no sculpture. Interior deep blue- 

 green, sutural plates white, sinus rather broad, convex in centre with a 

 central dark-brown spot and a yellow tinge on either side of it. The 

 anterior valve has eight slits, the edges of which are thickened and 

 upturned, the insertion plates lightly grooved. The median valves also 

 have the insertion plates grooved, and one slit. The posterior valve has 

 a thickened rib-like insertion plate. 



Colour : Ground-colour greenish-brown, irregularly barred with cream, 

 the sixth valve cream with irregular zigzags of the ground-colour, the 

 anterior valve uniform brown. 



* This and other numbers enclosed in parentheses refer to the list of literature at 

 end of paper. 



