CYAMIUM. 259 



tracing of them. You will see that in two of the figures 

 the tube is exserted : but the animal is rather shy in 

 extending it, and it can only be seen by watching the 

 opportunity. It is probably the anal siphon, as is sup- 

 posed to be the case in Lucina [Loripes], the branchial 

 siphon being either very short or only formed by a fold 

 in the open mantle, as in some other genera." I have 

 myself failed to detect any slender tube such as Mr. 

 Alder has described, although during the last two years 

 I have examined a great number of living and active 

 individuals on the spot and under extremely favourable 

 circumstances. Subjoined is the result of my observa- 

 tions, which were noted at the time of their being made, 

 with respect to the shape and position of the tube and 

 foot. The excretal or anal tube is small, button-shaped, 

 and almost sessile. It is situate on the upper part of 

 the posterior or broader side of the shell. This process 

 is formed out of a fold or contraction of the mantle, and 

 slightly separated by a raised edge from the long ventral 

 opening. It is occasionally protruded, but never to a 

 greater extent than the one-hundredth part of an inch. 

 When this takes place the lower side is higher than the 

 upper, and appears, when viewed sideways, like an ex- 

 ceedingly minute tooth or conical point. Being nearly 

 transparent, the raised edges cannot be seen, unless the 

 object is placed in relief on a black ground. The mouth 

 or orifice of the tube is roundish-oval and plain. I 

 repeatedly observed excretal pellets ejected from it. No 

 other tube or orifice was perceptible on the same side. 

 The ventral gape, occupying the middle of the open 

 valves, is very large and wide. It serves for the ad- 

 mission of food, as well as of water to aerate the gills. 

 There was always a current passing into it, charged 

 with animalcula. The edges of the mantle towards the 



