HYDROMEDUSAE. 737 



0. tenuis (Mayer), 1900. Tropical Atlantic; Florida. Syn. Halicalijx tenuis, Mayer (1900, 

 IX 63, Pis. v.— VI.). i.Halicalyx tenuis, Fewkes (1882, p. 277, PI. VII.). 



There is a disagreement in the descriptions given by Fewkes and by Mayer of Halicalyx 

 tenuis. Fewkes states that the medusa has twelve tentacles, uniform in shape, with a single 

 otolith at the base of each one. Mayer describes his specimens with two distinct kinds of 

 tentacles and a pair of sense organs at the base of each primary tentacle, and also with 

 many centripetal canals, which are not mentioned by Fewkes. Fewkes's specimen cannot be 

 an early stage because the gonads are described and figured, though it may be an inter- 

 mediate stage in growth. I can understand Fewkes's instituting a new genus for his species, 

 because it does not agree with the generic character of Olindias, and at that date the genus 

 Aglauropsis was very vaguely described on an incomplete description of a single species. 

 It is just possible that Fewkes's specimen belongs to the genus Aglauropsis. Mayer's 

 beautiful figures of Halicalyx tenuis show all the characters of an Olindias. 



Olindias singularis, species nova. (PI. LVI. fig. 2, PI. LVII. fig. 1.) 



Description. Umbrella hemispherical, with thick walls, about one and a half times as 

 broad as high. Stomach about half as long as the cavity of the umbrella: mouth with four 

 lips having a sinuous margin. Four radial canals : four to five blind centripetal canals in 

 each quadrant. Gonads on the outer half of each radial canal, and separated into isolated 

 papilliform clusters. Two kinds of tentacles ; primary tentacles which are carried outwards 

 and have their bases attached to the margin of the ex-umbrella, and secondary tentacles 

 which hang downwards from the margin of the umbrella. About 7 — 10 primary tentacles and 

 4 — 5 secondary tentacles in each quadrant. About 8 — 10 globular marginal bulbs containing 

 nematocysts in each quadrant. One internal sensory vesicle containing a single otolith at the 

 base of each primary tentacle. 



Size. Umbrella 13 mm. in width and 8 mm. in height. 



Distribution. Indian Ocean: Maldive Is., Suvadiva (Gardiner). 



The collection contains a single specimen in a good state of preservation. It mainly 

 differs from the species hitherto described in possessing only one sense organ at the base of 

 each primary tentacle, instead of a pair of sense organs. The possession of a pair of sense 

 organs has been considered by Haeckel to be a part of the generic character. I think that 

 the position of the sense organs, external (jr internal, and the number of sense organs had 

 better not be included in the generic characters, but would be of more use for specific 

 characters. Haeckel states that Olindias mulleri found in the Mediterranean has, in addition 

 to the internal paired sensory vesicles, a series of club-shaped ocelli situated between the 

 marginal bulbs. I have examined large adult specimens fi-om Naples and have failed to find 

 any ocelli. 



In Olindias singularis the primary tentacles are curved outwards from the margin of the 

 umbrella. Their bases are partly enclosed by an overgrowth of the ex-umbrella, to which 

 they are attached for a short distance. These tentacles have either oblong or short spiral 

 bands of nematocysts, and at their free end there is a claw-shaped termination, which has 

 its margin closely packed with very long nematocysts. The secondary tentacles are hollow 

 (like the primary ones) and hang down from the margin of the umbrella. They have a 

 large basal bulb and numerous bands of nematocysts, forming about three-quarter circular 



