Bh EXPLANATION OF PLATES. 
PARTS OF THE SHELLS. 
Mr.a. Margo anterior, anterior margin. 
Mr.p. Margo posterior, posterior margin. 
Mr. dx. Margo dexter, right margin. 
Mr.sn. Margo sinister, left margin. 
Pr. Peritrema, peritreme. 
P.anf.t. Anfractus inferior, lower whorl. 
T.ap. Teste apex, apex of the shell. 
aD: Testz basis, base of the shell. 
i: 5. Teste syphon, syphon of the shell. 
U. Umbilicus, umbilicus of the shell. 
EXTERNAL PARTS OF THE ANIMALS. 
Ap.l. Apertura lateralis, lateral aperture. 
B. Branchie, branchiz or gills. 
Dr. Dorsum, back of the animal. 
Lb. Labium, lip. 
Lb. i. Labium inferius, lower lip. 
Oc. Oculus, eye. 
Op. Operculum, operculum or opercule. 
Os. Os, mouth. 
12h Pes, foot. 
Pot Pedis latera, sides of the foot. 
Pr Pallium, mantle. 
Tn.s.  Tentacula superiora, superior tentacles. 
Tn. +. Tentacula inferiora, inferior tentacles. 
Tn. dx. Tentacula destra, right tentacles. 
Tn. sn. Tentacula sinistra, left tentacles. 
is: Respirationis syphon aut tubus, syphon or respira- 
tory tube. 
PLATE III. 
The figures in this and in all the following descriptive plates are 
explanatory of the external and internal structures of the Class 
Ginglymaconcha. 
Fig. 1. The left valve of Pholas Dactylus, containing the animal 
entire, the whole of the right valve being removed, except the 
umbonie portion. In this view the right mantle 1s seen entire, 
and also the right umbonic apophysis. 
‘Ar. u. The attachment of the right posterior muscle and the right 
