154 BRITISH PALEOZOIC ASTEROZOA. 



shafts as in Urasterella and Salteraster. The arrangement is similar to that in 

 TJrasterella except that one of the pair of adradialia immediately succeeding the 

 primary radialia is larger than the other, suggesting that the single interradial 

 plate in this position in Protarthr aster longimanus is the survivor of a pair of plates 

 one of which has been suppressed (see p. 163). 



The infero-marginalia are seen on the left and right arms of the photograph. 

 They are oblong, closely touching, and have a distinct transverse ridge. They 

 differ therefore in appearance from the same series of ossicles in S. asperrimus. 

 Just beneath the infero-marginalia of the right arm of the photograph may be seen 

 ridged plates which must be the adambulacralia. They are visible because this 

 arm is seen slightly in lateral view. 



R-.-_ £ 



Text-fig. 99. — Plan of the ossicles on a portion of the disc and arms of Salteraster (?) coronella. C, centrale ; 

 I. M., infero-marginalia ; i?., radialia; X., adradialia (paired interradialia). x 10. 



The plan of the ossicles shows a small interradial plate just proximal to the 

 infero-marginalia, which may be the apical surface of the odontophor. All the 

 apical plates are closely touching, without interspaces for the protrusion of 

 papulae. 



Measurements. — R : r : : 7 mm. : 2'5 mm. 



Horizon and Locality. — Lower Silurian (May Hill Sandstone), of Gunwick Mill, 

 near Africk, Malvern, Worcestershire. 



American Species of Salteraster. 



The following two species described by Schuchert as belonging to the genus 

 Urasterella, apparently really belong to Salteraster. 



U. grandis, Meek, described by Schuchert (85, pp. 180 — 182). — The form is 

 very large (R : r : : 93 mm. : 9 mm). Arms subcylindrical in outline. The rows 

 of adradialia are not differentiated (85, pi. xxvii, tig. G). On the disc the ossicles 



