DESCRIPTION OF PLATES, 9 — 11. 645 



Fig. 6 a, Acasta laevigata, tergum, internal view ; 6 b, another var. 



7 a, Acasta fenestrata ; 7 b, scutum, and 7 c, tergum, internal 



views. 



8 a, Acasta purpurata ; 8 b, scutum ; 8 c. tergum, internal views. 



9 a, Acasta sporillus ; 9 b, carino-lateral compartment (almost 



rudimentary) and lateral compartment, seen from within ; 

 9 c and 9 d, scutum and tergum, seen from within. 



PLATE 10. 



Genus — Tetraclita. 



Fig. 1 a, Tetraclita porosa, var. communis. 

 lb, ,, ,, ,, rubescens. 



lc, 

 Id, 

 le, 

 1/, 



1 h, 



nigrescens. 

 elegans. 



communis, young, with radii developed. 



,, ,, patellaris. 



„ basal edge of wall of shell. 



„ basal edge of wall of shell, var. elegans, 

 showing also the structure of one of the 

 rudimentary radii or sutures. 



1 i, „ ,, internal view of scutum ; 1 k, do. of tergum ; 



1 I, do. of scutum, var. ; 1 m, do. of 

 tergum, var. 



2 a, Tetraclita serrata ; 2 b, portion of external surface of wall, 



low down, near basis ; 2 c and 2 d, scutum and tergum, 

 internal views. 



3 a, Tetraclita rosea, scutum ; 3 b, tergum ; 3 c, whole shell ; 3 d, 



basal edge of wall of shell. 



PLATE 11. 



Genera — Tetraclita and Elminius. 



Fig. 1 a, Tetraclita purpurascens, var. with surface disintegrated, and 

 with the sutures united and obliterated. 



1 6, Tetraclita purpurascens, var. well preserved, with the 



radii developed ; 1 c and 1 d, scutum and tergum, internal 

 views. 



2 a, Tetraclita costata ; 2 b and 2 c, scutum and tergum. 



3 a, Tetraclita vitiata ; 3 b, basal edge of portion of wall ; 3 c and 



3 c?, scutum and tergum, internal views of; 3 e, tergum, 

 internal view, var. 



4 a, Tetraclita ccerulescens ; 4 b, scutum and tergum united, ex- 



ternal view ; 4 c and 4 d, scutum and tergum, internal 

 views. 



5 a, Tetraclita radiata; 5 b, scutum and tergum united, external 



view ; 5 c and 5 d, scutum and tergum, internal views. 

 G a, Elminius Kingii ; 6 b and 6 c, scutum and tergum, internal 

 views of; C d, tergum, var. external view of ; 6 e, tergum, 

 another var. internal view of. 



