80 BRITISH PALEOZOIC ASTEROZOA. 



Scliuclierfc places all the Ordovician and Silurian forms of tliis sub-family 

 provisionally or finally in one genus, Mesopalseaster. He also recognises three 

 Devonian genera — Spaniaatev, Schondorf, Mlomasfer, Schondorf, and Devonaster, 

 Schiichert. 



As in the case of the HudsonasteridjB (p. 68), the sub-family as defined 

 probably contains diverse lineages which are at the same parallel stages of 

 development. Thus — 



(1) There are almost certainly amongst the Ordovician and Silurian " Meso- 

 palgeasters " the early stages of the " Xtnasfer" lineage. 



(2) Deuonaster may be a late stage of development of an offshoot lineage. 



At present our knowledge of the forms is incomplete. Nevertheless, it seems 

 necessary to separate the British forms known to Schuchert as M. caractaci from 

 forms like the American M. shaferi, the liolotype of the genus Mesopalseaster. 

 I propose to name the new genus Caractacaster. Orally the species of Caracfa- 

 caster are almost in the '^ Hudsonaster '^ stage (Text-fig. 41, p. 82), although 

 apically accessory plates have been added. In the true " Mesopalmaster " the oral 

 surface has advanced well beyond the " Hvdsonaster " stage (Text-fig. 45, p. 85). 

 British species very closely similar to M. shafferi are found in the Upper 

 Ordovician (Ashgillian) of Scotland, but not in the British Caradocian or earlier 

 strata. These facts suggest that the culmination and migration of this genus 

 may have taken place in late Ordovician times (compare the corresponding details 

 for Promopalgpaster, p. 92). 



Genus CARACTACASTER, novum. 



Generic Characters. — Odontophor scarcely enclosed by the proximal infero- 

 marginalia. Plates of apical area only slightly swollen. Proximal supero-mar- 

 ginalia help to form boundary wall of disc. Madreporite present. 



Genoholotype and only species, G. caractaci, from the Ordovician of Wales and 

 the Welsh border. i 



Two American species, Mesopalseaster intermedins, Schuchert, and Meso- 

 palseaster {?) lanceolatus, Schuchert, have the odontophor in the same position 

 as Caractacaster. The apical surface of M. intermedius is unknown. The oral 

 surface of M. (?) lanceolatus is very distinct from that of C. caractaci (see p. 98). 



1. Caractacaster caractaci, Gregory sp. Plate II, fig. 4; Plate III, fig. 1; Text- 

 figs. 40, 41, 42, 43. 



1865. Palxaster caractaci, Salter, Cat. Fos.s. Mus. Practical Geology, p. 30 (nomeu nudum). 

 1880. „ „ Nicholson and Etheridge, Mon. Silurian Foss. Girvan Dist., Ayrshire,. 



fasc. 3, p. 321 (no description). 



