Tonna.] GASTROPODA. 315 



New Zealand specimens are smaller, and but rarely so much spotted 

 as Australian shells. 



In the Canterbury Museum there is a specimen of T. costata from 

 the Bay of Islands. It is no doubt an accidentally dropped specimen, 

 and does not belong to the New Zealand fauna. 



Fain. ARCHITECTONICID.E, H. and A. Adams. 

 Solar i idee, Chenu. Architectonidce, Gray. 



Animal with very large oval foot, notched in front ; tentacles 

 cylindrical, split throughout their length, thick, with eyes sessile on 

 swellings near their outer bases. Dentition variable. 



Shell depressed conic, turbinate or planorbiform ; aperture entire, 

 angular or subcircular ; lip and columella simple, interior without 

 nacre ; umbilicus wide and deep, and usually with crenulated margins ; 

 main sculpture usually spiral. Operculum corneous, spiral. 



KEY TO GENERA. 



A. Shell depressed conic, angular at the periphery, umbilicus 



with strongly crenulated margin . . . . . . ARCHITECTONICA. 



B. Shell turbinate, umbilicus moderate or wide, rounded at 



the periphery, margin of umbilicus slightly crenulated ; 



operculum elevated spiral . . . . . . HELIACUS. 



C. Shell subdiscoidal, flat or concave above, whorls carinated 



at the periphery, umbilicus keeled . . . . . . OMALAXIS. 



Genus 1. ARCHITECTONICA, Bolten, 1798. 



Architectonica, Bolten, Mus. Bolten. (2), 1798, 78. Type : Trochus perspec- 

 tivus, L. Solarium, Lamarck, 1799. 



Animal with a large foot, notched in front, and having a very 

 pronounced marginal fold ; head large, furnished with 2 tentacles, 

 which are short, thick, and cylindrical ; eyes on swellings near the 

 outer bases of the tentacles ; gill-cavity divided by a longitudinal 

 fold. 



Shell depressed, conic, angular at the periphery ; aperture sub- 

 quadrangular ; lip simple ; umbilicus with crenulated margins, spiral, 

 wide, and perspective. 



Distribution. World-wide, inhabiting warm seas. 



Fossil. Tertiary. 



Subgen. 1. ARCHITECTONICA, s. str. 

 Solar iorbis, Conrad, 1865. 



Surface of the shell strongly and closely sculptured longitudinally, 

 spirally ribbed and sulcate. Operculum corneous, paucispiral, with 

 the nucleus subexcentric. 



The teeth of the radula are long, spiniform, pronged, and without 

 a central tooth. A jaw is present. 



