98 [May, 



SUMMARY. 

 1. — Rareness. 



a. Paucity in mnnbers. h. Eestrictiou of rauo-eor /m&(7rt^ 



2. — Eareness may be clue to : 



a. Phylogenetic, h. Ontogenetic, factors. 



3. — Phylogenetic Factors. 



a. Distributional orisjin. b. Gradually increasing range. 



<*. Gradually decreasing range. d. Change of pliysiographical 

 e. Evolution of new forms. and climatic conditions. 



/. Relation to other organisms. (/. Past geological history. 



h. Difference in migrational /. Exceptional means of distri- 

 paths. bution. 



4. — OntootEnetic Factors. 



Almost invariably fundamentally climatic, reacting 

 a. Unfavourably on the organism, h. Unfavourably on its food supply. 

 r. Favoui'ably on its enemies. 



166, Bede Burn Eoad, 

 Jarrow-on-Tyne : 



January 23rd, 1917. 



A Halticid-heetle, Psijlliodes affinis Payk. (=^ Ma crocneina exoleta Curt.), 

 damaging the foliage of potatoes. — As we are endeavouring to grow as many 

 potatoes as possible during the present year, it is perhaps worth while 

 to call attention to an insect — not the Colorado potato-beetle this time — 

 that appears to have greatly damaged the foliage of older plants in the 

 vicinity of Stuttgart in 191.5. The insect in qiiestion, Psylliodes affinis 

 Payk., which is widely distributed in Britiiin, and is known in Germany 

 as the " potato earth flea-he(;tle," was included and figured by Ciu'tis 

 in his " Farm Insects " amongst the species affecting potato-crops, but his 

 account of the damage done by it mainly refers to Solatium dulcamara. The 

 German writei's, Tolz and Heikertinger, who have described the various stages 

 of P. affinis, state that the young potato-plants are not much injured by the 

 beetle or its larvae, but that great damage is done to the older plants by the 

 feeding of the adult. P. affinis feeds on various Solanaceae (Solanum, Hyoscya- 

 vius, and Atropa), but apart from Curtis's statement, I have seen no other 

 record of its attacking S. tuherostim in this country. The allied P. luteola Miilh, 

 rare in Britain, is also said by Bedel to attack the leaves and stems of potato 

 plants. I once saw it in great profusion at Larche, France, on willows, border- 

 ing ground cultivated with potatoes, but the beetles Avere doiibtless merely 

 resting on the trees. The above particulars concerning P. affinis are taken from 

 an abstract from a Stuttgart periodical, noticed in the "Review of Applied 

 Entomology" for March, 1917.— G. C. Champion, Horsell, Woking: April, 1917. 



