136 



(Fig. 62). It appears to open in some places through small pores on the 



inside of the rod. The rods of the other arms are quite smooth. 



While there is nothing remarkable in the structure of the skeleton thus 



far described, excepting the unusual feature of the canal in the postero- 

 lateral rod, the separate rod developed on the dorsal side along 

 the median line of the body represents quite a novel feature, 

 otherwise entirely unknown in Ophiurid-larvae. This extra rod, 

 the preoral rod, as it may be termed, proceeds from the up- 

 per end of the dorsal median process upwards to the anterior 

 V end of the body, where it bends over to the ventral side and 

 then proceeds downwards over the frontal area unto the pre- 

 oral band. While the dorsal part of this rod is only slightly 

 thorny, the part on the ventral side is provided with very 

 long side branches, so that it has the appearance almost of 

 a spinal column with its ribs. (The name coslatus refers to 

 this peculiarity). This remarkable skeletal rod supports the 

 unusually large preoral part of the larval body, which forms 

 like a large vault over the mouth of the larva. - - The ends of 

 the median process and the preoral rod nearly touch one an- 



Fig. 62. Part other, but do not join and remain separately movable. In this 



of postero- pi ace furthermore a quite small, styliform skeletal rod, the 

 lateral rod of 



Ophiopiuteus accessory rod, is found, which may perhaps have some lunc- 

 costatus, tion in connection with the movements of the oral lobe. 



5a ' '*' One specimen of this larva, fully developed, showing the 

 five lobes on the hydrocoel, was taken in the Red Sea, 17 40' N. 40 10' E. 

 12/XI, 1899. Besides there are two younger specimens, taken at the same 

 time, which may probably belong to the same species. The preoral rod 

 has merely an indication of side branches, and there is no accessory rod. 

 The backwards directed processes from the transverse rods have not yet 

 developed. The posterolateral rods are canaliculate unto the very points 

 in one specimen, not at all canaliculate in the other; but in this latter 

 specimen they are, upon the whole, somewhat abnormal. Both spec- 

 imens being young and in a poor state of preservation, it is impossible to 

 ascertain whether they belong to species a or to a separate species. 



Also from 25 miles S.E. of Minikoi (I/I, 1914) there is a specimen of 

 0. costatus, which probably belongs to species a; but it is in too bad a 

 state of preservation for definitely ascertaining to which species it belongs. 



Species b. (PI. XXI, Fig. 2). The size and general shape of the body 

 are as in species a. The arms are somewhat longer, the posterolateral 

 ones six times, the other arms about twice the body length, the antero- 



