BEVISION OF PALEOZOIC STELLEROIDEA. 93 



Interbrachial areas with single, large, hexagonal, axillary inter- 

 brachial plates. 



Adambulacral pieces quadrangular, fairly uniform in size for two- 

 thirds the length of the rays and then become gradually smaller 

 distally; there are about 15 in a column. A peculiarity , of this 

 species is that the ambulacralia do not continue around the axillary 

 interbrachials, but cease with the basal inframarginals. There are, 

 therefore, in M. caractaci no adambulacral oral armature pieces. 



Ambulacral furrows moderately wide, with as many rectangular 

 ambulacralia as there are adambulacrals, plus probably four more 

 in each column, and these continue around the axillary interbrachial. 

 Therefore, the oral armature consists entirely of ambulacralia. All 

 of these ossicles are directly opposite one another and have high 

 medial crests that are continuous across the ambulacral furrow. 

 Podial openings large laterally between the plates and the adambu- 

 lacrals. 



Locality and formation. Caradoc sandstone, Soudley quarry, 

 Church Stretton, England. The holotype, a split nodule, is in the 

 British Museum (Natural History), No. 48206; wax squeezes from 

 which the photographs have been made are in the United States 

 National Museum. Other specimens, Bather states, are in the Museum 

 of Practical Geology, London; these are from Marshbrook and occur 

 at a somewhat higher geological level. 



Remarks. Gregory wrote in 1899 that "the nearest ally of this 

 species is P. matutina (Hall)," but the illustrations here presented 

 wiU show that the relationship is with Mesopaldeaster shafferi and not 

 with Hudsonaster matutinus. 



Cat. No. 60606, U.S.N.M. 



MESOPAL^EASTER (?) ACUMINATUS (Simonovltsch). 



Asterias acuminatus SIMONOVITSCH, Sitzb. d. mat.-naturw. Classe Akad. Wiss., 



Wien, vol. 64, Abt. 1, 1871, p. 100, pi. 3, figs. 2-2d. 

 Asterias acwninata SCHONDORF, Palaeontographica, vol. 56, 1909, pp. 72, 109, 



pi. 11, figs. 7, 8. SCHONDORF, Jahrb. nassauisch. Ver. Naturk., Wiesbaden, 



vol. 62, 1909, p. 32, pi. 5, figs. 4, 5. 

 Roemeraster (?) acuminattis STURTZ, N. Jahrb. fiir Min., etc., 1886, vol. 2, p. 154. 



Actinally this small and slender species is nearly in harmony with the 

 generic characters of Paldeaster and Hudsonaster, differing only in that 

 the axillary interbrachial plates barely extend to the margin of the 

 disk, while in those genera they are prominent and marginal in the 

 axils. In Asterias acuminatus they are as yet not crowded so far orally 

 as in most species of Mesopalseaster. It is a difference of degree, not 

 of kind; therefore this species has more the actinal character of 

 Mesopalseaster than Hudsonaster. Ambulacral plates unknown. 



Abactinally Simonovitsch's species is said to have six columns of 

 tumid plates, all alike and persisting throughout the rays. If the 



