placing weak carbonate of ammonia about an inch from ilio 

 orifice the animal emitted bubbles of air and showed signs of 

 distress by movement and by pouring forth water from the 

 mantle. On immersing in water animals long exposed to the 

 air many bubbles of air rapidly escape, and then the siphon 

 became tranquil and full of water. In this state the animal 

 continued many days. Magenta dropped into the water 

 gradually spread out and was drawn imperceptibly into long 

 threads of currents towards the siphon. Magenta dropped 

 into the siphon was not emitted for a long time, and then 

 thoroughly diluted and in fine streaks. All these facts tend 

 to show that respiration is accomplished by no muscular 

 movements, but by the ciliated surface, of the simple sac of 

 which the lung is composed. 



In the circumstance of breathing air and water the animal 

 has this peculiarity in common with all our fresh water 

 mollusca. I am not aware that this has been ascertained of 

 our Siphonariae, and certainly it was not known that its 

 anatomy corresponds in every respect with the fresh water 

 pulnionifera. The lingual ribbon of this and the following 

 species I find to be in keeping with its pulmoriferous 

 chai-acter. Mr. Woodward in his Manual (p. 286, 2 edit.) 

 says, " The inoperculated air-breathers, without known excep- 

 tion, have rows of similar teeth with broad bases resembling 

 tesselated pavement, whose crowns are recurved, and either 

 aculeate or dentated." I may quote also on this subject the 

 observations of W. Thomson (Annals Nat. Hist., 1851, p. 

 86). He says, " The tongue of the Pulmonobranchiata 

 generally is a thin expansible membrane, two-thirds or three- 

 fourths of which is rolled into a tube ; the posterior end of 

 this tube is closed, while at its anterior extremity the remain- 

 ing portion of the membrane is expanded into a flattened or 

 spoon shaped form which plays against the edge of the horny 

 upper jaw, thus acting more as an under jaw than a tongue. 

 It is enclosed in the muscular head and connected with the 

 oesophagus at the anterior end of the tube, the extended 

 upper portion of the oesophagus forming the roof of the 

 mouth, while the expanded surface of the tongue covers the 

 lower part of the mouth. From the junction of the oeso- 

 phagus and tongue the former passes backward and leaves 

 the head at the upper part, while the latter takes at once a 

 downward and backward direction, and protrudes its closed 

 end at the lower part of the head. The tongue when laid 

 open is of the same width throughout. It is covered with a 

 vast number of plates with tubercles which are curved back- 

 wards. ' The plates are in rows which are straight in the 

 antero-postero diameter, but variously curved or angular 

 transversely. The number of teeth is not constant in indi- 



