CLASS I 



ASTEROIDEA 



240 



Family 2. Astropectinidae. 



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

 about twenty Recent 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 schlüteri Stürtz, 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 ^ c; 



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 ^'<255ig^öifc^tfQJiiMttÖ?SyMBiKI^^ i b 

 Aspidosoma (Fig. 352) has been 

 very carefully studied by Schön- 

 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 Falaeonectria ^^^^^^^^^ petaloüUs Simon. Lower Devonian; NieHler- 



and PalaeOStella Stürtz, and Tricha- lahnstein, Nassau. ^, Ventral aspect natural size^ Arm 



. ' viewed from the dorsal side. "^ a7„„4.™i *■ ^f „^r„ 



steropStS Eck. enlarged (after Simonowitsch). 



C, Ventral aspect of arm, 



Pentagonaster (;!) 

 impressns (Quenst.). 

 Upper Jura ; Reiohen- 

 bach im Thäle. A, 

 Supero - marginal 

 plate. B, Infero- 

 inarginal plate. C, 

 Plate with supposed 

 pedicellariae (after 

 Quenstedt). 



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 large 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 Saiteraster Stürtz, from 

 the Silurian of England. Perhaps Protasteracanihion Stürtz, 

 from the Devonian of Germany, also belongs here. 



Family 5. Goniasteridae ( = Pentagonasteridae). 

 These Starfishes are generally recognisable by their flattened 

 form, Short rays, very large disk, and very conspicuous 

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

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

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



