8 DESCRIPTION OF THE ANIMAL OF TRIGONIA 



quadrilateral (properly the abdomen), and a lower pointed part (the 

 true foot), the two being set at right angles to one another. 



The first portion is sharp-edged and slightly pectinated posteriorly, 

 marked by a groove bounded by two folded lips anteriorly. The 

 second portion is slightly pectinated along its lower edge, pointed 

 anteriorly, prolonged behind into a curved process, where it joins the 

 superior portion. 



Visceral mass. — ^The mouth opens by a very short oesophagus into 

 a wide pyriform stomach, surrounded by a dark dendritic liver. The 

 stomach narrows into a long intestine, which descends for the whole 

 length of the abdomen, and forms one or two loops in the substance 

 of the generative gland ; then passes up again above the stomach, 

 penetrates the heart, and passing between the two small lateral 

 muscles of the foot, terminates in the anus. 



[Plate I.]' 



Fig. (i). View of the animal with the right valve of the shell removed, and the right lobe 

 of the mantle turned back. (/, mouth ; b, anus ; r, filamentous appendages of 

 mantle ; d, gill ; e, grooved superior part of foot. 



Rg. (2). View of the animal from behind, with the valves separated. Letters as before. 



Fig. (3). Visceral cavity laid open, a, stomach, surrounded by the liver ; b, intestine ; 

 c, heart ; d, generative gland. 



' The word Plate accompanied by a number and printed within brackets refers throughout 

 to the plate-number assigned to each plate in the present reprint of Huxley's papers, and 

 not to the original numbering of the plates as published in transactions or journals. — Eds. 



