MONOGIiAPH OF .lArANESE OPHIUROIDEA. :91 



protected doi'sal side of the arms. Further, there are two types 

 of primitive ophiurans differing in the embryonal condition of the 

 vertebrae, one being the Phrynophiuridan type and the other the 

 Laemophiuridan. In the Phrynophiuridan type, the distal vertebrae 

 are divided into halves by a single fusiform pore, the middle 

 parts of the halves being widely separated from each other. 

 These vertebra? are proved to be present in Ophioheliis, Ophiogerofu 

 Astrogeron, Ophiosciasma, Opliiohyalus, Ophiomyxa, Ophiostiha, &c» 

 In the Laemophiuridan type, the distal vertebrae are divided into 

 halves by a series of small pores, the halves being connected with 

 eacli other by a series of bridges between every two pores* 

 These vertebra3 are present in Mlcrophiura, Ophiothamnus, Ophio- 

 logimus, Amphiactis, &g. In AsfrophJura, the vertebrae of the free 

 arm joints are divided into halves by a moniliform pore, the 

 halves being closely set against each other, so that the condition, 

 though rather near to the Laemophiuridan type, is intermediate 

 between the two types. 



Key to the families of Lœniophiurida, 



A — Disk and arms of slender build, the disk scales or plates, as well 

 as arm plates, being not very stout ; the genital plate and scale on 

 either side of a radius articulate with each other, instead of being 

 soldered together; vertebrae not very stout, often divided into 



halves OpMacanthidœ. 



A A — Disk and arms of very heavy build, the disk and arm plates being 

 very stout ; the genital plate and scale on either side of a radius 

 are firmly soldered together ; vertebrae very stout, always entire, 

 thougli til« ventral median groove is very prominent . . HemieuryolidcB . 



