ME1HT&E. 33 



Not long ago Professor Hartlaub informed me in a letter that he had obtained a 

 new Medusa from Norway with open sensory pits, but thought, after all, that it must 

 be Thaumantias pilosella of Forbes. An exchange of letters and specimens proved 

 that the specimens were Thaumantias pilosella, and Prof. Hartlaub adopted the name 

 Cosmetira for the genus. 



Cosmetira pilosella is a very common Medusa during the summer months on the 

 British coasts, and occasionally it occurs in vast shoals. 



The Medusa described by Prof. Maas (1893) under the name of Ilalopsis megalotis 

 belongs to this genus. 



I have also placed provisionally in this genus a new Antarctic species called 

 Cosmetira frigida, a description of which is given on p. 35. 



TIAROPSIS, Agassiz, 1849. 



Generic Character. Mitrocomidse with four radial canals ; with eight sensory pits ; 

 with an ocellus adjacent to each sense organ ; without marginal cirri. 



This is the oldest genus of the family, and contains about six species. Mr. Torrey 

 (1909) has recently split the genus into two. For the species with tentacles which 

 are all alike the old name Tiaropsis is retained, but for those species with two 

 kinds of tentacles, large and small (some of which are no doubt young stages), he 

 proposes a new genus called Tiaropsidium. The one character common to all the 

 species, and it is a conspicuous character, is the presence of a definite ocellus adjacent 

 to the sensory pit. I consider that it is best to keep all the species with this character 

 together, and that another genus is not really wanted. I must leave for another 

 occasion the critical examination of the species, which are at present as follows : 

 Tiaropsis multidrrata (M. Sars), 1835, T. diademata, Agassiz, 1849, T. mediterranea, 

 Metschnikoff, 1886, T. rosea, A. Agassiz and Mayer, 1889, T. punctata, Mayer, 1900, 

 T. davisi, Browne, 1902, and T. Mseyi (Torrey), 1909. 



MITROCOMELLA, Haeckel, 1879. 



Generic Character. Mitrocomidse with four radial canals ; with sixteen sensory 

 pits ; with marginal cirri. 



This genus probably contains only a single species, namely, M. polydiadema 

 (Romanes), 1876, which has been found on the coasts of the British Isles and Norway. 

 On a casual examination it is easy to mistake this Medusa for Cosmetira pilosella, 

 unless the number of sense organs be counted. I think the species described by me 

 in 1903 under the name of Mitrocomella fulva had better be placed as a synonym of 

 M. polydiadema. 



MITROCOMA, Haeckel, 1864. 



Generic diameter. Mitrocomidae with four radial canals, with numerous open 

 sensory pits, with marginal cirri. 



