PALASTERTSCUS. 177 



real kinship was with Solaster and Valvaster, and as these were put in the recent 

 family, the Echinasteridae, he founded for it a new family, the Palgechinasteridae. 

 Gregory (1900) founded the family Palasteriscidse for Palasteriscus and Echin- 

 asterella. Schuchert (1914) enlarged Gregory's family by the addition of 

 Cheiropteraster and Loriolaster. The structure of these latter three genera 

 will be dealt with later. They have a very different structure from that of 

 Palasteriscus. 



The only species is Palasteriscus devonicus, Stlirtz, from the Lower Devonian 

 slates of Bundenbach, Germany. 1 Three specimens, including Stiirtz's type, are 

 preserved in the British Museum (Nat. Hist.) nos. E. 3466 (the type), E. 3407, 

 and E. 5026. A drawing of the ambulacralia and adambulacralia of E. 3407 is 

 given here (Text-fig. 119, p. 174) to show the exact correspondence of these 

 ossicles with those of Platanaster ordovicus. There are no infero-marginalia in 



Text-fig. 122. — Apical view of the ambulacralia of Palasteriscus devonicus. Am., ambulacral ; Ar., forwardly 



projecting peg. x 10. 



this species as there are in the earlier form. The photograph of the apical 

 side of E. 5026 (PI. XIV, fig. 4) shows transverse rows of paxillaa and broad 

 petaloid arms — characters not shown in Stiirtz's figures drawn from the type. It 

 is possible that the form of the arm, as seen in the photograph, is somewhat 

 over-emphasised by dorso-lateral compression, and that originally the arm was 

 more rounded. 



The apical surfaces of the ambulacralia show that the dorsal longitudinal 

 muscles had increased their power beyond that observable in the Ordovician 

 species. The closely fitting plates of Platanaster ordovicus (Text-fig. 120, p. 175) 

 are replaced by ossicles which have a distinct peg-and-socket fitting. The 

 development is comparable to that observed in Schuchertia (compare with 

 Text-fig. 126, p. 186, and Text- fig. 127, p. 187). Measurements give R as 

 approximately 140 mm. The large madreporite is 22 mm. long. 



i hoc. cit., vol. xxxii (1886), p. 95, p], xiv, fig. 1 ; vol. xxxvi (1890), pp. 223-225, pi. xxviii, fig. 23, 

 pl. xxix, fig. 24. 



24 



