118 PROVISIONAL AID TO THE STUDY OF TASMANIAN MOLLUSCA. 



umbo. Some bivalves, as in Pholas and Barnea, have one or 

 two accessory plates near the hinge, while the Chitons have 

 eight imbricating valves like an articulated limpet, and are 

 termed multivalves. The conical or flatly conical shells of the 

 limpet group are usually simple and not spiral. The following 

 are a list of terms applied to the principal distinguishing 

 character of shells generally. 



UNIVALVES. 

 Fosm op Shell. 



I, (a) Eegularly spiral. 



1. Elongated, subulate, elevated 



2. Turreted, turricuiate, an elongated 



shell with the whorls angulate or 

 shouldered on their upper part . . . 



3. Cylindrical, pupiform 



4. Short, bucciniform 



5. Eusiform, spindle-shaped 



6. Confabulate, short, with shouldered 



whorls 



7. Globular, rounded 



8. Depressed, lenticular ... 



9. Discoidal, having the form of a 



disc or quoit ... 



10. Convolute, aperture about as long 

 as the shell, nearly or quite con- 

 cealing the spire 



11. Trochiform, pyramidal, conical, with 

 a flat base 



12. Turbinated, conical, with rounded 



13. Cone shaped, obconie ... 



14. Eew whorled, whorls rapidly in- 



creasing 



15. Many whorled, whorls slowly or 

 gradually increasing 



16. Ear-shaped ... 



17. Subulate, awl-shaped ... 



18. Acicular 



(5.) Irregularly spiral, evolute ... 

 (c.) Tubular, tusk-like, tooth-like 

 (d.) Boat-shaped, slipper-shaped... 

 (e.) Conical or limpet-shaped 

 (f.) Multivalve and imbricated .. . 



• See accompanying Plate. 



^Example fig. 



No. 



32 



33 



44, 45 



5 



2,3 



16 

 19 



21,22 



24, 25, 26, 28 



11 



9,18 

 27 



... 13, 36 



... 12,39 

 23 

 38 

 40 



31 



46 



... 14,15 



57, 58, 59 



47 



