64(5 DESCRIPTION OF PLATKS, 12, 13. 



PLATE 12. 



Genera — Elminius and Pyrgoma. 



Fig. 1 a, Elminius modestus ; 1 b, scutum, internal view ; 1 c, tergum, 



internal view ; 1 d, do., tergum, var. ; 1 e, do., tergum, var. 



2 a, Elminius plicatus ; 2 b, basal edge of portion of wall of shell ; 



2 c and 2 c?, scutum and tergum, internal views of: 2e and 

 2/, scutum and tergum, internal views of, var. 



3, Elminius simplex ; shell. 



4 a, Pyrgoma Anglicum ; 4 b and 4 c, scutum and tergum, internal 



views. 



5 a, Pyrgoma cancellatum, shell, seen from above ; 5 b, shell seen 



on the under side : 5 c and 5 d, scutum and tergum, external 



views : 5 e and of, scutum and tergum, internal views of. 

 6, Pyrgoma Stokesii, shell imbedded in coral. 

 Ja, Pyrgoma conjugatum, shell, external view of; 7b, scutum 



and tergum, calcified together, seen from the outside ; 7 c, 



do., internal view of. 



PLATE 13. 



Genera — Pyrgoma and Creusia. 



Fig. 1 a, Pyrgoma grande ; 1 b, scutum and tergum, calcified together, 

 external view of; 1 c, scutum and tergum, internal view 

 of; Id, the tw 7 o scuta and terga, external view of, seen 

 from above, having their natural position, when closed. 



2 a, Pyrgoma milleporse, shell viewed from above ; 2 b, internal 

 view of, showing the sheath ; 2 c, scutum and tergum, 

 united, external view of; 2 d, scutum, var. external view 

 of; 2 e, scutum, internal view of; 2f, tergum, internal 

 view of. 



'da, Pyrgoma dentatum shell, external view of; 3 5, scutum, 

 var. 1, external view of: 3 c, tergum, var. 1, external view 

 of; 3 d, tergum, var. 2, external view of; 3 c, scutum, var. 

 3, external view of; 3f, tergum, var. 3, external view of; 



3 (/, scutum and tergum, var. l, joined together, internal 

 view of. 



4 a, Pyrgoma crenatum, scutum, external view of, showing the 

 great depending adductor plate and large occludent ledge ; 



4 b, tergum, external view of. 



5a, Pyrgoma monticularice, external view of; bb, another speci- 

 men, internal view of; d c, another specimen, external 

 view of; 5 d, portion of circumference of shell, viewed 

 externally, much magnified, showing the outer lamina, 

 and the irregular, longitudinal septa ; 5 e, another speci- 

 men of the same, with the longitudinal septa more regular ; 

 ') f t scutum and tergum completely calcified together, 

 external view of. 



