86 AXEL A. OLSSON 



by Hanley in the same tray as the type. This second specimen was thought 

 by Hanley to have been subsequently added by Sir J. Smith, the pur- 

 chaser of the Linnean collection in order to further elucidate the species. 

 Cuming identified this specimen as Area maculosa Reeve. It is the opinion 

 of this author, that this second specimen represents Linnaeus species and 

 proves antiquata a Red Sea or Indian Ocean species. 

 A broader definition of the genus is as follows: 



Shell small or large, solid or of medium texture, porcellaneous, rhombic 

 to elongated, with equal valves or if unequal, the left valve is larger, its 

 margin overlapping the other, and the sculpture of the two valves may be 

 somewhat discrepant. Umbones prominent, anterior of the middle, with the 

 small, prosogyrate beaks pointing inward or inrolled over a cardinal area 

 of variable height, low or high trigonal in shape and extending on both 

 sides of the beaks. The surface of the ligamental and cardinal area may 

 be smooth or grooved by tent-shaped, or more rarely, by straight longi- 

 tudinal lines. Hinge line straight, with numerous teeth in a graduated series, 

 small or minute in the middle, larger and divergent at the extremities. Sur- 

 face sculptured by strong ribs which are plain, noded, or divided, the in- 

 terspaces deeply grooved. Sculpture of the two valves similar or more or 

 less discrepant. 



Key to the subgenera of Anadara 



I. Cardinal area covered completely by the ligament. 



A. Cardinal area is elongate and rather narrow, smooth or grooved with 

 tent-shaped lines. Shell ovate to elongated, equivalve as to shape, 

 convexity, and sculpture. 



1. Cardinal area smooth or vertically striated, the ligamental grooves 

 generally absent or of erratic development. Ribs bi-or quadriplicate in 

 the adult. 



Subgenus Anadara, sensu stricto 

 Red Sea and Indo-Pacific. 



2. Cardinal area covered by tent-shaped ligamental grooves. 



2a. Posterior side not depressed, winged, or emarginated. 



Subgenus Diluvarca 



2b. Posterior side more or less impressed, emarginated. 



Subgenus Rasia 



B. Cardinal area high, trigonal, set-off by deep, marginal grooves. 



3. Shell solid, equivalve. Internal margins strongly fluted. 



3a. Ribs relatively few and wide. Beaks large, strongly coiled, Cardita-like. 

 Periostracum coarse, black. 



Subgenus Senilia 

 African 



3b. Ribs quite numerous, noded, the beaks normal. 



Subgenus Larkinia 



3c. Ribs less numerous, mostly smooth. 



Subgenus Gtandiarca, new subgenus 



