Invertebrate Gallery of the Indian Museum. loi 



which is the madreporic plate) with their adjacent mouth- 

 shields, each mouth-plate bearing a series of teeth and 

 tooth-papillae ; and radiating from the mouth-shields, the five 

 " arms, " or rays, with their large transverse under-plates. 

 The rays, however, have no open ambulacra] groove as 

 they have in the Star-fishes, but the ambulacral groove is 

 completely closed in by a series of ventral or "super- 

 ambulacral" plates, between which and the side-plates the 

 tube-feet emerge. 



The under surface of the disk, beyond the mouth-shields, 

 is thickly beset with little spinelets, and on this surface, 

 on either side of the base of each arm, is seen a broad 

 fissure known as the genital cleft, through which the 

 reproductive glands discharge their contents. 



The Ophiuroidea live at all depths, from between tide- 

 marks down to the abysses of the ocean. They appear 

 to flourish best in the seas of the tropics, as is illustrated 

 in the Andaman Sea, where the trawl is never worked at 

 depths of 100 to 250 fathoms without bringing up scores 

 of specimens [Ophiacantha, Ophiocamax^ Ophioglypha), 

 and where at low-water the pools of the coral reefs are 

 often full of writhing masses of brittle-stars [Ophtothrix^ 

 Ophiocoma, Ophiomaslix), 



The Ophiuroidea consist of two families — the Ophiuridse 

 or typical forms, in which the rays are simple and un- 

 branched ; and the Astrophytidx^ in which the arms are 

 usually branched. 



jst. The OphiuridsS are represented in the exhibited 

 collection by specimens of the following genera, all from 

 the Indian Seas : — 



From the reefs -.—Pectinura, Ophiolepis, Ophiozona, 

 Ophiocnida, Ophiophragniics, Ophiocoma, Ophiarthrum^ 

 Ophiomastix, Ophiothrix, Ophiocnemis. 



From the great depths : — Ophiernus, Ophioglypha^ 

 Ophiomusium, Ophioca max» 



2nd. The Astrophytidae are represented by several forms 

 from the depths, none of which, however, appear to corre- 



