23S The hish NaturalisL Noveuiber, 



NOTES. ON TIIR DISTRIBI'TION OF IRISH FRESHWATER 



(.AIITES HYDRACHNID.E). 



BY J.N. IIALBRRT, M.R.I. A. 



The mites in .cifeiieral are among the most widely distributed animals, 

 and the Hydrachnid^ are no exception to the rule. The winged insect 

 hosts to which these mites attach themselves during their parasitic larval 

 stage are very effective agents in the spreading of the species. It has 

 been suggested that the freshwater mites may be divided into two great 

 faunistic groups, according to the nature of the waters they inhabit, 

 and these two divisions serve equally well for a preliminar}" grouping of 

 the Irish species from a distributional point of view. One group con- 

 tains those widely distributed species inhabiting the standing and 

 slowly-flowing waters of lowland lakes, ponds, etc., of a comparatively 

 high temperature. To the second group belong those interesting forms 

 found iu waters of a constantly lower temperature, especially those of 

 cold highland lakes and streams. These forms possess a more restricted 

 range, typicall}' northern and alpine in character, reaching their 

 greatest development in Scandinavia and the alpine regions of Central 

 Europe. 



THE develop:\ient of LITTORINA. 



BY W. M TATTKRS.\rj., M.SC. 



The eggs of L. litorea, each enclosed in a hat-shaped capsule are laid 

 freely on the shore, not aggregated together in a gelatinous mass. 

 There aretrocosphere and veliger larval stages. L. Utorea lives low down 

 in the zone of Laminaria and Fitciis serraliis. L. ohtusaia lives higher among 

 Fitcus: vesicidosus ; its larva leaves the egg as a veliger, L. ritdis and 

 L. neritoides which live near high-water mark are both viviparous. 

 Thus the genus exhibits three stages in the evolution of land from 

 marine moUusca, with the suppression of larval forms with successive 

 specialisations of habitat. 



THE VAvSCULAR SYSTEM OF vSTYLODRILUS. 



BY ROWT.AND SOUTHERN, B.vSC. 



The genus Stylodrilus has hitherto been distinguished from other 

 European genera belonging to the Oligochcnete family Lumbriculidae 

 by the complete absence of the blind contractile appendages of the blood- 

 vessels which are so characteristic of this family. The new species in 

 vestigated (but not yet described) from the River Annalee, County Cavan, 

 undoubtedly belongs to the genus Stylodrilus, but differs from all other 

 species in the posse.ssion of very simple contractile appendages to the 

 dorsal vessel. These blind .sacs are restricted to the posterior end of the 



