32 HWVARD T. BROWNE. 



FAMILY MITROCOMIDvE (Haeckel, 1879), Torrey, 1909. 



Character of the Family. Leptomedusae with open sensory pits on the velum, 

 containing otocysts. 



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

 sensory pits, but circumstances arose which compelled me to lay aside the work before 

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

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

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

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

 The hydroid genus Lafoea has no connection with the Medusae belonging to the 

 Mitrocomidse. Messrs. Maas and Torrey include the genus Halopsis in the family 

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

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

 mention is made of the sense organs being open pits. Before Halopsis can be included 

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



The family consists of the following genera : Cosmetirella, Cosmetira, Tiaropsis, 

 Mitrocomella and Mitrocoma. 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. Mitrocomidse with four radial canals ; with eight sensory 

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



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

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

 among the Eucopidse. The only real difference between Cosmetirella and Phialella 

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



COSMETIRA (Forbes, 1848), Hartlaub, 1909. 



Generic Character. Mitrocomidse 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 

 Cosmetira 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 Euchilota, which has closed sensory vesicles and belongs to the Eucopidse. 

 Subsequently I noticed that the sense organs were open pits, and realised that the 

 species would have to be removed to another genus, for which I selected Forbes' 

 name of Cosmetira. 



