PLATE XV 



SCAPHOPODA 



i. Diagrammatic sketch of the structure of Dentalium : a, posterior 

 opening of the alimentary canal ; a.m., anterior margin of. the mantle ; 

 /., foot; h., head; I.., liver; m. } mouth; m.c, mantle cavity; s., shell; 

 s.m., shell muscle; t., tentacles. 



2. Dentalium elephantinum , Linn. 



PELECYPODA 



3. Unto pictorum, Linn., with right valve and mantle lobe removed : 

 A., anterior end; P., posterior end; a. a., adductor muscles; b., 

 branchial opening; /., foot; L, ligament; 0, mouth; p.p.. pedal 

 muscles ; t, palpi ; u., umbo ; v, posterior end of alimentary canal ; 

 x, accessory pedal muscle. 



4. Myatruncata, Linn, (after Forbes), showing the only partly retractile 

 siphons covered with a tough, wrinkled prolongation of the penos- 

 tracum. 



5. Lepton squamosum, Mont, (from a drawing by Alder), showing the 

 mantle (m.) with its fringe of filaments, of which one in front (t.) is very 

 long ; /. is the foot ; s. the siphon. 



6. Pisidium amnicum, Mull, (original by S. P. Woodward) In this 

 genus the anterior end of the shell is, by exception, longer than the 

 posterior, the foot (/.) is protruded through the opening (b.) in the 

 mantle, which also serves to convey the water to the gills, the stale 

 water passing out through the single siphon s. 



7. Psammobia vespertina, Chemn. (after Poli), showing the great 

 length of the two siphons: r.s., respiratory siphon; e.s. s excurrent 

 siphon ; /., foot. In this bivalve also the mantle margin is fringed. 



8. Pecten varius, Linn., shown rather widely open : br., branchiae or 

 gills; 7n., fringed mantle or "curtains." The black dots in the 

 margins of the mantle next the shell are the " eyes." 



9. Dreissensia polymorpha, Pallas, or Zebra Mussel : b., byssus by 

 which it anchors itself; /., foot. The arrows distinguish the incurrent 

 and excurrent siphons. 



%* Fig. 1 drawn by Miss G. M. Woodward. The others from drawings 

 by S. P. Woodward. 



