Clare Island Survey — Fresh-ivater Entomostraca. 46 3 



A number of slight variations from the typical forms have been noted, 

 some of which are referred to under the notes on the species, but nothing 

 apparently of real importance, except in one specimen from Clare Island of 

 what seems to be Ctuithoctmptus Mrticornis. In this case the furca and their 

 setae, as shown on Plate I, fig. 10, are completely changed from the usual 

 type to something unlike what is found in any known species. It may be 

 merely an example of malformation, although, as the structures are perfectly 

 symmetrical, it more probably represents a distinct mutation. 



A comparison of the Entomostracan faunas of the different sections of 

 the area comprised in the Survey brings out a number of interesting facts. 

 Considering first the relation of Clare Island to the country around Clew Bay, 

 we find that whereas the total number of species of the Cladocera recorded 

 from the island is only about one-half the number from the mainland, the 

 number of Copepoda is very nearly the same, and the number of Ostracods 

 about two-thirds. The actual figures are as follows :— 



Cladocera. Copepoda. Ostracoda. Total. 



Clare Island, 24 19 10 53 



Mainland (including Achill), 48 21 15 84 



The Clare Island fauna is mainly noticeable, as perhaps was to have been 

 expected, for negative rather than positive characters. It is true that a few 

 species have been obtained there which have not hitherto been found in the 

 mainland area (e.g. Cyclops bisetosns, Canthocamptus Mrticornis, C. praegeri, 

 n. sp., Nitocra spinipes, and Cypris obliqua ?), but these, with the exception of 

 the new species, about which nothing can be said, may be confidently expected 

 to occur on the mainland also. On the other hand, there are some rather 

 remarkable absences from the Clare Island list, viz.,Diaphanosoma, Bosmina, 

 Alonopsis, and Polyphemus. It seems almost impossible to imagine that these 

 absences can be without significance, as representatives of the genera mentioned 

 are fairly common on the mainland. What the significance may be is not 

 known, but it may be surmised to be connected with the means of dispersal. 



The Achill Island list contains the following species which have not 

 been noticed in other parts of the area covered by the survey -.— Latona 

 setifera, Holopedium gibberum, Ilyocryptus sordidus, Cyclops nanus, Zimnicythere 

 inopinata. As none of these, however, can be considered as common species, 

 it is not possible to draw any inferences from their presence in Achill and 

 apparent absence elsewhere. The absence of Simocephcdus vetvlus, a very 

 common species in all parts of the country, is rather surprising, but may be 

 only accidental. 



The Westport-Castlebar list shows the following characteristic species : — 

 Ceriodaphnia ptdchella, C. affinis, Bosmina longirostris, Pleuroxus trigonclln-<. 



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