32 i:i>\VAi;i» T. r.ROWNK. 



Family MITROCoMID.K (Haeckel, 1H79), Toirey, 1909. 



Clutracti'r of the FamHi/. — Leptomcdusiu with open seusory pits ou the velum, 

 contuiniug ot<x-yst8. 



In the summer of 1908, I began a revision of the Leptomedusje with open 

 sensory pits, Imt rircumstaiices arose which compelled me to lay asiile the work l)efore 

 the critical examination of the species was finished, and even now it must he deferred 

 for another communication. Prof. Mmis, in 1893, practically laid the foundation of 

 the family, which he called the Lixfoeidaj ; but I agree with Mr. Torrey (1909) that 

 Mitrocomidaj is a better name to use, and it wa.s that which I was going to adopt. 

 The liydroid genus Lafoea has no connection with the Mcdusio belonging to the 

 Mitrocomidaj. Messrs. Maas and Torrey include the genus y/t/Ayw/.v in the family 

 with open sensory pits, but in the descriptions given by Prof. Agassiz (1865) and 

 Mr. Fewkes (1888) of Ilnlopsis ocellata, which is the type species of the genus, no 

 mention is made of the sense organs being open pits. Befijre Udlopsis can be included 

 among the Mitrocomid* the structure of the sense organs must be re-investigated. 



The family consists of tlie following genera: — Cosmetirelht, Cosmetini, TInropsis, 

 Mitrocomella and Mitrocinna. I give the characters of the genera and just mention 

 the species, but some of the latter have not been critically examined. 



COSMETIRELLA. 



Generic Character. — Mitrocomid:e with four radial canals; with eight sensory 

 pits ; without marginal cirri ; and witliout ocelli adjacent to the sense organs. 



This new genus is established to receive a new Antarctic species, dcscribeil on 

 p. 34, under the name of Cosmetirella simplex. This genus corresponds to PhialeUa 

 among the Eucopidae. The only real difference between Cosmetirella and PhialeUa 

 is that the former has open sensory pits, and the latter closed sensory vesicles. 



CosMETiRA (Forbes, 1848), Hartlaub, 1909. 



Generic Character. — Mitrocomidsu with four radial canals ; with eight sensory 

 pits ; with marginal cirri. 



The type species of the genus is Cosmetira pilosella (Forbes). It was originally 

 described by Forbes under the name of Thaumantias pilosella, and he proposed 

 Cosmetii-a as a sub-generic name. He never mentioned the existence of sense organs, 

 which I found some years ago, when (1896) I temporarily placed the species in the 

 genus Eucltilota, which has closed sensory vesicles and belongs to the Eucopidse. 

 Subsequently I noticed that the sen.se organs were open pits, and realised that the 

 species would have to bo removed to anr)ther genus, for which I selected Forlies' 

 name of (\)smetir<t. 



