Mfti<4*(H*ocoek <m the Animal of Myochama anomioides. %^\ 



.Qlther/tBQOdifications may exist, but these are all that have come 

 under my observation. 



The body or visceral mass [j) of Myochama is largely deve- 

 loped, and projects downwards and forwards from between the 

 branchial plates ; it is somewhat compressed and inclined to a 

 triangular form, with a small conical foot (A) rising abruptly in 

 front from the inferior extremity. The liver is of a pale brown 

 colour, and is composed of numerous small lobules, irregular in 

 form and size, which appearing all over the surface of the visceral 

 mass give to it a peculiar tessellated appearance. The intestine 

 passes round the external surface of the posterior adductor 

 muscle, and terminates within the anal chamber close to the 

 base of the exhalant tube as a simple tubular anus. 



From this description of the animal of Myochama, it would 

 seem evident that the proper place in the arrangement of this 

 genus is with the Anatinidce, if we may take Cochlodesma as a 

 type of that family. The former agrees in every essential cha- 

 racter with this latter genus : the siphonal tubes are long and 

 narrow, the mantle is closed, and there is a single gill-plate and 

 a rudimentary gill-plate on each side arranged exactly in the 

 same manner. Chamostrea differs from Myochama chieily in 

 having short, wide tubes, and in the rudimentary gill-plate 

 having its dorsal margin free. 

 ?i ' 



EXPLANATION OF PLATE XL 



Tig. 1. General view of the animal of Myochama anomioides, the left man- 

 tle-lobe laid open : — a, anterior slope ; h, posterior ditto ; c, ven- 

 tral margin ; d, pedal orifice ; e, orifice leading to inhalant tube ; 

 /, orifice in the septum dividing anal and branchial chamber j 

 g, exhalant tube; h, inhalant ditto; i, fourth aperture leading 

 into branchial chamber with a needle passed through it ; j, body 

 or visceral mass ; k, foot ; I, palps, the superior overhanging the 

 mouth ; m, perfect gill-plate ; n, rudimentai-y gill-plate ; o, line 

 dividing the two portions of the gill-leaflet ; p, ovary ; q, posterior 

 adductor muscle ; r, anterior ditto. 



Fig. 2. Front view of visceral mass : — a, liver ; b, foot ; c, c, margins of 

 gill-plates; d, mouth; e, e, superior pair of palps; /,/, inferior 

 ditto. 



Fig. 3. View of siphonal tubes : — a, inhalant tube ; b, exhalant ditto ; 

 c, fourth or small aperture leading into branchial chamber ; d, d, 

 margins of mantle-lobes forming a recess for the accommodation 

 of the tubes; e, posterior adductor muscle. 



Fig. 4. External view of pedal orifice : — a, pedal oiifice; b, b, margins of 

 mantle-lobes ; c, c, c, anterior adductor muscle. 



