124 PROVISIONAL AID TO THE STUDY OF TASMANIAN MOIXUSCA. 



Example" fig. 

 No. 



Pectinated, resembling the teeth of a 



comb. 

 Pinnated, winged. 



Quadrangular, having four right angles. 

 Eadiately, rayed or ribbed, rays or ribs 



springing from umboe, in the 



direction of limb or margins ... (52) 



Eidge, the upper part of a slope. 

 Scalloped, indented at the edges. 

 Serrated, having teeth like a saw. 

 Serrulated, very minutely serrated. 

 Sub-arcuated, somewhat arched. 

 Sub-diaphanous, somewhat transparent. 

 Transverse, breadth greater than length. 

 Trapeziform, shaped like a trapezium. 

 Trigonal, having three angles, deltoid. 

 Turgid, swollen. 

 Ventral margin, the margin opposite 



the hinge-margin. 

 Ventricose, inflated or swelled in the 



middle. 

 Umbo, the beak or round part which 



turns over the hinge. 

 Note. — Many of the terms relating to the sculpture of 

 univalves, are also applicable to the sculpture of bivalves. 



Length, Beeadth and Thickness. 

 The hinge line of bivalves indicates the 



direction of the length of the shell, 



and the actual length is the 



maximum distance between lateral 



margins. 

 The breadth is the greatest diameter 



measured transversely to length. 

 The thickness is the greatest diameter 



of an imaginary line passing 



through one or both valves. 



Ligament. 

 The valves of the Pelecypods are bound 

 together by a ligament, (49 c ) and 

 usually articulated by a hinge 

 furnished with interlocking teeth. 

 The shell is closed by (either one 

 or two) powerful, adductor muscles 

 (53 a ) but opens spontaneously by 

 the action of the ligament when the 

 animal relaxes, and after it is dead. 





