156 



lactea (Sluiter) ater n. sp. 



minima n. sp. violacea n. sp. 



The study of these species shows that the genus, though hydri- 

 formis in several respects differs distinctly from the other species, 

 is one of the most homogeneous genera of the Synaptinae, and 

 the examination of the numerous beautifully preserved specimens 

 at hand (ca. 330) throws a desirable light on the range of variation 

 within the species, and on the value of the systematical characters. 



The larger part of the specimens have a rather characteristic 

 colour, and even the irregularly mottled species as recta, striata, 

 psara and denticulata, may be separated by the coloration. 



The number of tentacles is within the species usually very 

 constant, and very rarely it varies with more than a single tentacle. 

 Nearly all the species have 10 or 13 tentacles, and only hydri- 

 formis and reciprocans are known with certainty to have another 

 number 12 and 15. The number of digits varies from 4 — ca. 30 

 pairs. Some species, as bandae and hydriformis, are characterized 

 in having relatively few digits and others, as psara, in having many 

 digits; but as the number of digits is evidently increasing with 

 age, it is not a character of much classificatory value. 



The presence or absence of a web between the digits, is, though 

 it may be very difficult to distinguish in preserved specimens, 

 probably one of the most important characters. Internal characters 

 which may be used for classification in this genus are: the shape 

 of the calcareous ring, the cartilaginous ring, the stone-canal and 

 the madreporite. The number of the polian vesicles varies from 

 three to more than fifty, but it is, as the number of the digits, more 

 or less increasing with age. The gonads are in all the species but 

 hydriformis and indivisa, distinctly branched, and in hydriformis 

 where they are club-shaped in all the small specimens at hand 

 (especially in those from Tobago), the larger specimens (especially 

 those from Bermuda and Jamaica) seem to have branched gonads. 

 The ciliated funnels (Fig. 15. 9) are in all the species found on 

 the mesenteries, and are of the same size and shape as in the 

 genera Synapta, Opheodesoma, Euapta and Polyplectana. 



The calcareous deposits are anchors, anchor-plates and, in all 

 but one species, miliary granules. Rods are wanting in all the 

 oriental species, but present in the tentacles of hydriformis. The 



