KEY-TAHLH. 



ll'.t 



III. — Marginals generally wedge-shaped, high, spine-pits very shallow or absent. 

 Pedicellariae when present with five valves round a deep central 

 depression. Pi/ciiiaster. 



1. Platos of maximum heit^bt, 10 



mm. P. angugtatug. See PI. 

 IX, fig. 1 a. 



2. Platos of maximum lieifjlit, 20 



mm., p -shaped iu profile. P. 

 senonensis. Text-fig. 23, (a) 

 outer view of marginal, (b) 

 interior view of mar<i;inal, (c) 

 side view. 



Text-fio. 2.3. 



Text-fio. 24. 



3. Plates very thick, often oblong, 

 not wedge-shaped. P. craggtis. 

 PI. XXIX, fig. 3, exterior view 

 of marginal. Text-fig. 24, side 

 view of marginal. 



rV. — Marginal plates breast-plate-shaped. Stanranderaster (see p. 125). 

 A. With .spine-pits. 





1. Spine-pits fairly coarse. S.hul- 



hiferug (commonly occurring). 

 Text-fig. 25. 



2. Spine-pits medium. S. bipvnc- 



tatvs (only one specimen 

 known). Text-fig. 26. 



Text-fio. 25. 



Text-fio. 26. 



