166 Mr. J. Blackwall on Cases of Defective and 



traordinary organic modifications, in consequence, perhaps, of 

 their less frequent occurrence, have been almost entirely over- 

 looked, the purport of the present communication is to illus- 

 trate by a few examples the importance which cases of the 

 latter description possess in relation to physiology and syste- 

 matic arrangement. 



1. In March 1835, I found, under a piece of rock in a wood 

 near Oakland, Denbighshire, an adult female Theridion fiVipes^ 

 Blackw., exhibiting an anomaly in organization which I never 

 witnessed before in this order of animals ; it had a supernu- 

 merary eye situated between the two small ones constituting 

 the anterior intermediate pair, the total number of eyes pos- 

 sessed by this individual being nine, and their arrangement 

 symmetrical. 



2. An immature female Thomisus cristatus, captured at 

 Oakland on the 20th of July 1835, had the two lateral pairs 

 of eyes only, the four small intermediate eyes being altogether 

 wanting, not the slightest rudiment of them being perceptible 

 even with the aid of a powerful magnifier. The size of this 

 spider was about one-fourth less than that of an adult. 



3. In the summer of 1836, I took an adult female Lycosa 

 campestris in my father's garden at Hendre House, Denbigh- 

 shire, which had a short but perfectly-formed supernumerary 

 tarsus connected with the base of the tarsal joint of the right 

 posterior leg on its outer side. 



4. An adult male Lycosa Cambrica, Blackw., taken in a 

 marshy piece of land in a wood near Oakland in May 1839, 

 was quite destitute of the right intermediate eye of the ante- 

 rior row. 



5. I captured an adult female Epe'ira inclinata at Oakland 

 on the 29th of August 1842, which was entirely without the 

 left intermediate eye of the posterior row, and the right inter- 

 mediate eye of the same row was not half the usual size. 



6. An adult female Cmiflo atrox, Blackw. {Clubiona atrox, 

 Walck.*), taken near Hendre House on the 14th of Septem- 

 ber 1842, wanted the left intermediate eye of the posterior 

 row. 



7. A collection of spiders made by Mr. Hamlet Clark near 

 Towcester, Northamptonshire, in the autumn of 1842, and 

 obligingly submitted to my inspection, contained an adult 

 female Epeira inclinata^ whose right intermediate eye of the 



* For the circumstances which have led to the separation of Clubiona 

 atrox and other species from the Drassidce and Theridiidce, and to the esta- 

 bhslnnent with them of the new family Cmiflonida;, see the Transactions of 

 the Linnaean Society, vol. xviii. p. G06 et seq. 



