1922. No. 5. 



ARIONIDAE OF NORWAY. 



7 



a closer examination should be made. The common figures are not always 

 reliable, but a revision will perhaps aftbrd interesting results. 



Internal characters. In order to give a brief account of the 

 anatomical characters, reference is made to figure 2, which represents the 

 chief organs of Arioii atrr, but slightly simplified. The description alone 

 will indicate what is common to all Arioiis. 



The main mass of the internal organs is situated in the primary 

 body -cavity, into which open the arterial vessels. When isolated from 

 other organs, the alimentary system proves to consist of four tracts 

 or courses (/ — 4), the first of which is formed by the buccal mass, or 

 pharynx, the wide oesophagus (ocs) and lastly the short stomach [st.], whilst 



J'.O'. 



e.-c 



Fig 3. Diagram of radular teeth. 

 b. pi. basal plate, c. epithem, c.-c. ectocone, ni.-c. mesocone, s. c. secondary cusps. 



the three following tracts {2 — 4) form the narrower intestine opening into 

 the pulmonary aperture. These four tracts of the digestive system are 

 twisted up in a manner suggesting the visceral spiral in the shell-bearing 

 forms. The interstice between this system of tracts running backwards and 

 forwards, is almost entirely occupied b}- the digestive gland or "liver", 

 consisting of two lobes ; the left one is situated most posteriorly, forming 

 the hinder end of the visceral spiral, whilst the right one [r. d. gl.) is larger 

 and according to its anterior position has its opening into the stomach 

 slighdy advanced in relation to that of the left lobe (7. d. g/.) 



Upon both sides of the anterior part of the oesophagus is situated a 

 pair of salivary glands {s. gl.) from which on each side a salivary duct 

 opens into the buccal cavity. On the bottom of the latter we find the 

 radnla or lingual ribbon with its numerous small teeth projecting backwards; 

 all of them of the same type as is usual in several families of pulmonata 

 (fig. 3). The longitudinal mid-line of the radula is occupied by the sym- 

 metric central, median or rhachis teeth \o\, and on both sides are the un- 

 symmetrical lateral teeth (first row: /I which without a marked transition 



