Modiolarca.} PELECYPODA. 897 



Animal. Couthouy, in U.S. Expl. Exp., xii, 459 ; S. P. Woodward, 

 A.M.N.H. (2), xvi, 26. " 



Anatomy. Pelseneer, Voy. " Belgica," 44. 



Type in the Mus. Hist. Nat., Geneva. 



Hab. Aucldand Islands (fide Pelseneer) ; Macquarie Island (A. 

 Hamilton). Also Kerguelen, Marion. South Georgia, Falkland Islands, 

 Tierra del Fuego, South Patagonia. 



Remarks. The shell is usually found attached to the large floating 

 kelp Macrocystis. 



The animal moves with considerable rapidity, as follows : The foot 

 is doubled, so that its point is brought to its base ; it is then extended 

 to great length, carrying a byssal thread and attaching it to the object 

 towards whichit is moving ; by a sudden contraction the shell is jerked 

 forwards the length of the thread ; this operation is repeated until 

 the desired spot is reached, when it is there anchored by a number of 

 threads thrown out in various directions. These threads are very 

 elastic, and are found to proceed from the cavity at the base of the 

 foot. (Couthouy.) 



Fam. CRASSATBLLITIDJE, Ball. 



Animal having a triangular, compressed, canaliculate foot ; mantle 

 perfectly open, without anal siphon, or forming only a single orifice, 

 the anal ; margins of mantle papillate posteriorly ; labial palps tri- 

 angular, of moderate size ; gills unequal, the outer ones semilunar, 

 the inner ones larger, especially in front. 



Shell equivalve, thick, subtrigonal, the valves always somewhat 

 unequal and usually more or less rostrate, the beaks compressed, 

 erect, or hollowed behind ; ligament internal, more or less obsolete ; 

 resilium large, wholly internal, attached at each end to a chondrophoric 

 pit in the hinge-plate behind the cardinal teeth ; lateral teeth and 

 sockets usually alternated in the valves ; the hinge-plate heavy, flat ; 

 the posterior cardinal in the right valve very small or obsolete, with no 

 distinct socket in the opposite valve. 



Lower Cretaceous to Recent. 



SYNOPSIS OF GENERA. 



A. Shell moderately large, subtrigonal, solid, concentrically 



sulcate. Right valve with 2 cardinal teeth in front of 

 the resilifer, the posterior stronger ; left valve with 2 

 cardinals, the anterior stronger . . . . . . CRASSATELLITES. 



B. Shell small, thin, resembling Mactra, smooth. Right valve 



with 2 diverging cardinal teeth, meeting at summit ; left 



valve with 3 cardinal teeth, the median A-shaped . . CYAMIOMACTRA. 



C. Shell small, smooth, cardinals similar to those of Cyamio- 



mactra, but with a number of small lateral lamellae in 



front and behind, crenulating the margins . . . . PERRIEKINA. 



D. Shell small, fairly solid, trigonal, higher than long, radiate 



or concentrically sculptured. Right valve with 1 tri- 

 angular massive cardinal ; left valve with 2 divergent 

 cardinal teeth . . . . . . . . . . CUNA. 



29 Moll. N.Z. 



