A 

 MONOGRAPH 



OF THE 



LAND AND FRESHWATER MOLLUSCA 



OF THE 



BRITISH ISLES. 



Phylum MOLLUSCA Cuvier. 



(Malacozoa, Elainville ; Palliata, Latreille ; Heterogangliata, Owen ; Otocardes, Haeckel ; 

 Saccata, Hyatt ; Tetraneura, Schimkewitsch). 



The Mollusca (mollis, soft) are animals with soft and fleshy bodies, covered 

 by ciliated epithelium, containing numerous interspersed cells which abun- 

 dantly secrete the mucus which is so characteristic a feature of the group 

 and gives the body its suppleness and viscosity. 



They possess a cephalic region in which are located most of the organs 

 of special sense, a pallial region which develops or secretes the shell, and a 

 pedal or ventral region which constitutes the locomotory organ. 



Internally they present distinct digestive, cojlomic and circulatory cavi- 

 ties and scattered nerve centres, and primitively were bilaterally symmetrical 

 in their organization. 



Class GASTROPODA Cuvier. 



(Paracephalophora, Elainville ; Cephalophora, Macalister ; Glossophora, pais, Lankester ; 

 Cephala, Reeve ; Univalvia, Fischer). 



The Gastropods (yao-njp, stomach ; ttoS- foot) are the most typical of the 

 molluscan phylum, possessing the distinctive characteristics of the group in 

 the greatest degree and showing the least affinity to other phyla. 



Their chief features are a ventral and sole-like reptatory foot; a distinct 

 head ; a well-developed odontophore, armed with numerous transverse rows 

 of recurved teeth ; a hollow and more or less conical shell which may be 

 spirally coiled and external, or reduced to the merest vestige and concealed 

 within the tissues. 



Sub-Class ANISOPLEURA Lankester. 



(Gastropoda, Pelseneer ; Platycochlides, Ihering). 



The Anisopleura (a, not ; i'o-os, equal ; irXevpd, sides) are characterized by 

 the asymmetry of their organization, due to the torsion and semi-rotation the 

 visceral sac has undergone, which has transferred the respiratory and excre- 

 tory organs from their original posterior position to an anterior and lateral 

 one, aud also led to the diminution or even complete atrophy and loss of 

 the primitively left auricle, the left kidney, and the left moiety of other of 

 the paired organs of the body. 



Order EUTHYNEURA Lankester. 



(Platymalakia, von Ihering ; Pulmonata, Fischer ; Monoecia, Troschel ; Adelapneumona, Gray ; 

 Pulmonifera Inoperculata, Woodward ; Inoperculata, Reeve ; Saccobranchia, Leach). 



The Euthyneura (evOvs, straight ; vevpov, a nerve or tendon) embrace those 

 land, freshwater, and marine gastropods in which the twisting of the visceral 

 nerve-ring, characterizing the Streptoneura, has become obliterated by the 

 partial detorsiou the visceral sac has since undergone, and is also noticeable 



25/5/02 



