134 



are smooth, excepting a pair of small thorns sometimes found in the lower 



part of the anterolateral rods. 

 There are some specimens of this larva from off Taboga, in the Gulf 



of Panama, taken in November 1915. None of them are so far developed 



that the hydrocoel has 

 begun to form the pri- 

 mary lobes, and none of 

 them are in a very good 

 state of preservation, but 

 it was possible to give 

 a — sUghtly restored 

 — figure of the larva, 

 the comparison of the 

 different specimens in 

 hand making it easy to 

 ascertain the correctness 



Fig. 59. Skeleton of Ophiopluteus of Ophiocoma, species c. of the figure. 

 29%. Letters as in fig. 55. 



It is a very note- 

 worthy fact that the 

 only other Ophiuroid- 

 larva known to have vi- 

 bratile lobes is the larva 

 of Ophiocomina nigra, which — although it has recently^) been removed 

 from the genus Ophiocoma to which it was hitherto referred — is, evidently, 

 related to the Ophiocomidse and must probably be referred to that family. 

 The skeleton of that larva differs, however, markedly from that of the 

 Ophiocoma-lsLYya, the transverse rods -and end rods not forming a "hnk" 

 as in the latter, but being of the type usual in Ophiurid larvse. This 

 difference in the skeleton from that of the Ophiocoma-lavya is an addi- 

 tional proof of the necessity of removing the species nigra from the genus 

 Ophiocoma. 



Fig. 60. Posterolateral rod of same larva. *"Vi 



Ophiopluteus costatus nova lorma. 



This larval type is eminently characteristic through the unique feature 

 of having a separate median skeletal rod supporting tlie high frontal 

 area. The body skeleton is of the compound type, with a median ventral 

 and dorsal process from the transverse rods. The posterolateral arms are 



1) Th. Mortensen. Notes on some Scandinavian Echinoderms, with descriptions of 

 two new species of Ophiurids. Vid. Medd. Dansk Naturh. Forening. Bd. 72. 1920, p. 50—54. 



