45 4 Proceedings of the Royal Irish Academy. 



ss. " Helga," both in Blacksod Bay and Clew Bay. For the identification of 

 the Ballynakill and Blacksod and Clew Bay specimens I am myself responsible. 

 Species new to Ireland are marked with an asterisk. They number seventy, 

 and, in addition, four species, which appear to be new to science, are 

 described. 



COPEPODA GYMNOPLEA. 



Family CALANIDAE. 



Calanus helgolandicus (Cls.). — Better known under the name of C.finmarchicus, 

 which has, however, in recent years been reserved for the slightly 

 different and larger form which inhabits the Norwegian seas. G. helgo- 

 landicus forms, in the spring and summer, immense swarms all along the 

 west coast of Ireland, which extend seawards for from ten to twenty 

 miles, and form the main food of the spring mackerel on their arrival on 

 the coast. It seems to require water of a moderately high salinity for 

 its development, but penetrates into the bays and harbours when driven 

 shorewards by a westerly wind. 



Paracalanus parvus (Cls.). — Common along all the west coast, both in the 

 open sea and in bays and harbours. 



Pseudocalanus elongatus (Boeck). — Very common both in the open sea and 

 in bays and inlets, and often occurs in shoals. 



Calocalanus styliremis Giesbr. — An oceanic species, taken off Shark Head 

 in May and August, 1901. 



Clausocalanus arcuicornis (Dana). — An oceanic species, taken three times in 

 the beginning of 1901, off Clare Island, Inishturk, and Inishbofin. 



Ctenocalanus vanus Giesbr. — An oceanic species, taken once off Inishturk in 

 June, 1901. 



Chiridius armatus (Boeck). — An oceanic species, taken once off Shark Head 

 in April, 1901. 



Bradyidius armatus Giesbr. — Taken off Clare Island, 42 fathoms, in a bottom 

 tow-net in February, 1901. It is a bottom-haunting species usually 

 found on muddy ground. 

 *Stephos Scotti G. O. Sars. — Taken occasionally in Fahy Bay, Ballynakill, in 

 1901. 



Scolecithricella minor (Brady).— In a bottom tow-net off Shark Head, 54fms., 

 in July, 1901. Probably should be regarded as an oceanic species. 



Diaixis pygmaea (Scott).— In tow-nettings taken off Cleggan in 1901, one to 

 two miles from shore, scarce. 



