CLASS I 



ASTEROIDEA 



249 



Family 2. Astropectinidae. 



This is one of the largest families of Recent and Mesozoic Phanerozonia, 

 about twenty Eecent genera being known. The ambulacral ossicles are 

 opposite but that seems to be the only difference from the Palaeasteridae. 

 The type-genus, Astropecten Gray (Fig. 349), occurs in the Lias and later 

 Mesozoic, and is still a large and widespread genus. It is quite possible that 

 some Paleozoic forms are nearly related, if not actually congeneric, as for 

 example, Astropecten schlilteri Stiirtz, from the Devonian. The lower Silurian 

 Siluraster Jaekel is also very probably one of this family. 



Family 3. Aspidosomatidae. 



This family is characterised by alternate ambulacral ossicles and large 

 interradial areas. The rays are more or less petaloid or tapering, and the 

 disk is large. All of the known 

 forms are from the Paleozoic and 

 their structure is not only incom- 

 pletely known, but there is the 

 widest difference of opinion in inter- 

 preting such characters as are dis- 

 tinguishable. The , type -genus 

 Aspidosoma (Fig. 352) has been 

 very carefully studied by Schon- 

 dorf. As a result of these studies, 

 he proposed a new class called 

 Auluroidea. The structure of 

 Aspidosoma shows, however, that 

 it is probably a phanerozonate Star- 

 fish. Allied genera are Falaeonedria 



and lalaeOStella Stiirtz, and Tncha- lahnstein, Nassau. ^, Ventral aspect, natural size, i;, Arm 

 , _ . -pi 1 ' viewed from the dorsal side. C, Ventral aspect of arm, 



SteVOpSlS IliCK, enlarged (after Simonowitsch). 



^v4^>-' 



Fid. 352. 

 Aspidosoma pctalokles Simon. Lower Devonian ; Nieder- 



Family 4. Taeniasteridae. 



In this family, which is also confined to the Paleozoic, 

 the disk is very small and the rays are long and tapering. 

 The adambulacral plates are lai^ge and marginal in position. 

 The marginal plates bear spines on their free ends. The 

 principal genera are Taeniaster and Stenaster Billings, from 

 the Lower Silurian of Canada, and Salteraster Stiirtz, from 

 the Silurian of England. Perhaps Prof aster acanthioii Stiirtz, 

 PentagonasterCi) from the Devonian of Germany, also belongs here. 



ipre^siis (Quenst.). '' ° 



1/nip 



Upper Jura ; Reiehen- 

 bacli im Tliale. A, 

 Supero - marginal 

 plate. B, Infero- 

 marginal plate. C, 

 Plate with supposed 

 pedicellariae 

 Quenstedt). 



Family 5. Goniasteridae ( = Pentagonasteridae). 



These Starfishes are generally recognisable by their flattened 

 (after form, short rays, very large disk, and very conspicuous 

 marginal plates. The family is a large one, with more than 

 forty Recent genera, and its limits are ill defined. It first appears in the 

 Jurassic, and it is well represented in Cretaceous strata. The genus Pentagonaster 



