MOLLUSCA, G29 



Chitonellus strudus.—'Wia Striated Chilouellua. Plate Ixxvi. fis- l^t- Kacli 

 valye with strias radiating- from its apex ; tlip margins serrated ; tlie base <>t 

 the last valve obtuse. 



ORDER v.— PTEROPODA. 



Animals destitute of any foot for locomotion, and of arms for Beizing tlieir 

 prey ; provided with two opposite and similar fins fitting them for swim, 

 niiiig; body free and ttoatini^. This order contains six g-enera, namely, — 

 I. Pueumodermon ; 2. Cymbulia ; 3. Limacina; 4. Cleodora; 6. Clio; G. Hy- 

 al*a. — Of which we have given the follo«inif representations. 



Cijmbulia Peronii.—Perua's Cymbulia. Plate Ixxvi. 6g. G. Somewhat 

 (•elatinous, or cartilaginous; very transparent crystalline ; oblong, pointid 

 at the vertex, truncated at the base ; general shape like a Turkish slipper. 

 Two inches long. Inhabits the Mediterranean. 



Limacina iiclicialis.— The Helix-like Limacina. Plate Ixxvi. fig. II. Jhin, 

 fragile, spiral ; the volutions united in a discoid form. Half an inch in dia- 

 meter. Inhabits tlie North seas. 



Cleodora pyramidata.— The Pyramidal Cleodora. Plate Ixxvi. tig !>. Py- 

 ramidal, triangular; of a gelatinous or cartilaginous substance, very thia 

 and transparent; aperture obliquely truncated. Inhabits the American 

 seas. 



IbjalcEa tridentata.— The Tliree-Toothed Hyala;a. Plate Ixxvi. fig. 1?. 

 Transparent, horn-coloured, globular ; posteriorly tridentate ; summit and 

 tuo posterior sides open ; very finely striated transversely. Three-fourtlis 

 of an inch long. Inhabits the Mediterranean. 



CLASS II.— CONCHIFERA. 



Animals soft with articulations, destitute of head or organs of vision, and 

 always fixed within a bivalve shell ; having external branchiae ; a simple cir- 

 culation, and a unilocular heart. 



Lamarck divides this class into the two following orders ; — I. Monomy- 

 AUiA, with one muscle of attachment ; shell exhibiting interiorly but one 

 subcentral muscular impression. IL Di.mvaika, having at least two muscles 

 of attachment; the shell exhibiting interiorly, two separate, lateral, mus- 

 cular impressions. 



OIIDEJJ I. — AIONOMYAIRA. 



Contains Thirty-one Genera. 



1. LingHla; ?. Terebratula; X Orbicula ; 4. Crania; :>. Discina ; 6. 

 Birostrates; 7. Calcola; 8. Hadioletes; 9. Sph^rulites ; 10. Anomia ; 11. 

 Placuna; 12. Vulsella; IXOstrea; \i. Gryphaea ; Vo. Podopsis ; 16. Spon- 

 dylus; n Plicatiila; IS. Pecten ; 19. Plagiostoraa ; 20. Lima; 21. Pedum ; 

 1'2. Melcagrina; 2.S Avicula; 24 Malleus; 25. Perna; 2G. Crenatula; 27. 

 Pinna; 28. Mytiius; 2!». Modiola ; 30. Hippopus; 31. Tridacna.— Of which 

 we have figured the li>l!owing species ■ — 



