288 



ME. W. E. COLLINGE ON THE VAKIATION OF THE 



species, and Miers (4) was o£ a similar opinion. The late Dr. Biidde-Lnnd, 

 however, whose ripe experience and wide acquaintance with the terrestrial 

 species of this Order made his judgment so valuable, placed the greatest 

 reliance upon these organs (1 & 2) . 



Restricting my remarks to the genera occurring in the British Isles, 

 an examination of the oral appendages shows that in most of them the form 

 of the mandibles and 1st and 2nd maxillse are very similar, e. g., the two 

 maxillae in such widely separated forms as Oniscus asellus, Linn., Pliiloscia 

 miiscorum (Scopoli), Cylisticus convexus (de Geer), and Armadillidium vulgare 

 (Latreille) ; and linking these together, we have a large series of Continental 

 forms in the same genera, so that a perfect gradation can be shown to exist. 



Whilst working upon our British species, and also those of other countries, 

 I have noted that there is a considerable amount of variation in the oral 

 appendages according to the age of the specimen, and further, that other 

 variations occur, due, in all probability, to the nature of the food, environment, 

 etc. This being so, it seemed desirable to examine a fairly large number of 

 examples of representative species, and the results obtained considerably 

 lessen, in my opinion, the value of these organs as characters for generic and 

 specific distinction. 



The shape of the head, antennae, the mesosomatic' segments, the telson, and 

 uropoda I A'vould regard as of primary value ; that of the thoracic appendages 

 as of secondary, whilst the value of the abdominal and oral appendages as 

 diagnostic features I believe to be very much less. 



I have "only arrived at this opinion after examining a considerable number 

 of specimens of a fairly representative series of species. 



II. Species Examined. 

 The species examined and the number of examples and variations and the 

 times they occurred are as follows : — 



No 

 Species. . " , 

 ^ examined. 



No. of 

 Variations. 



No. of times 

 occurred. 



1. Lig a oeeanica, Linn 36 



4 

 1 

 13 

 7 

 1 

 4 



b 



7 



9 

 39 

 22 



5 

 20 



8 ' 



2. Trichoniscus roseus (Koclij 48 



3. Oniscus asellus, Linn 112 



4. Porcellio scaber, Latr 86 



5. „ Icsvis, Latr 3t) 



6. Poi cellionides pruinosus (Brandt) 68 



7. Armadillidiuvi vulgare (Latr.) *>' 



439 



33 



110 



Unless otherwise stated all the variations occurred on both sides of the body. 



