DESCRIPTION OF THE ANIMAL OF TRIGONIA 7 



I add the description of tlie animal given by the French naturaHsts 

 for comparison : — 



" L'animal a le manteau ouvert dans les trois quarts de sa circon- 

 ference inferieure. II est frange sur ses bords, avec de petites taches 

 ou hinules blanches qui alternent avec des stries rayonn^es. On voit, 

 au sommet de ce manteau, les impressions denticul^es de la charniere, 

 ■et en avant et en arriere, les muscles qui unissent les valves. Le pied 

 est grand, robuste, securiforme, tres recourb^ en arriere, tranchant et 

 denticul6 sur son arete, de chaque cote de laquelle sont des laciniures 

 au tiers anterieur seulement. II ne nous a pas paru se dilater comme 

 dans les muscles. Les branchies sont grandes, libres, subtriangulaires, 

 en pointe, reposant, de chaque cote de la racine du pied, leur doubles 

 lamelles. Les palpes buccaux sont excessivement petits, reunis dans 

 une partie de leur etendue. L'anus est a I'extremite d'un court 

 pedicule. La disposition du manteau et le manque de tubes rap- 

 prochent ce mollusque de celui des Nucules, dont il differe cependant 

 par la disposition des branchies et la brievete des appendices de la 

 bouche." 



Description of Trigonia. 



The mantle-lobes are rounded and plaited, to correspond with the 

 ribs of the shell. The edges of the mantle are marked with white 

 spots ; posteriorly, opposite the anus they are provided with short 

 convex appendages. The mantle-lobes are disunited throughout, not 

 joining until they reach the upper surface of the posterior adductor, 

 some distance above the anus. 



The gills are somewhat triangular, extending backwards almost 

 horizontally on each side of the visceral mass. Each gill is formed 

 of three stems, fixed at one extremity, free and pointed at the other, 

 and giving attachment throughout their whole length, on one side to 

 depending filaments, which become shorter as they are more posterior. 

 The filaments are formed of a tubular horny thread, supporting on 

 one side a broad membranous fringe. I could perceive no trace of 

 vessels in this fringe, but it appeared to be covered by an epithelium 

 (ciliated .''). 



The mouth is placed at the anterior and superior part of the 

 animal, between two thickish horizontal lips. The labial tentacles are 

 two on each side, rather long, lanceolate, and slightly pectinated. The 

 anus is placed posteriorly and superiorly between the gills, and just 

 about the posterior adductor muscle. 



The so-called "foot" is composed of two portions, an upper and 



