Bibliographical Notices. 101 



tui'es in the generally-accepted scheme of classification of the order 

 Aranete. This scheme, of which Dr. Thorell is the most able 

 exponent, depends upon the fact that a classification of the webs 

 according to their form corresponds closely with a classification of 

 the spiders based upon the sum of their most obvious structural 

 features. With the rival scheme *, which is established upon the 

 existence in otherwise dissimilar genera of those curious organs 

 known as the crihellum and calamistrum — a scheme for which 

 Dr. Bertkau has said all that is to be said — we need not further 

 deal. It will be sufiicient to state that Dr. McCook, rightly in our 

 opinion, adopts the views of Dr. Thorell, and associates with the 

 Orbitelariae the aberrant genera Uloborus, Hyptiotes, and TJierklio- 

 soma. 



But a noticeable circumstance connected with this matter is that 

 although, as above stated, a natural classification of the webs 

 coincides with a natural classification of their makers, when the 

 Aranese as a whole are considered, yet the principle is found not to 

 apply if an attempt be made to extend it to the suborder now under 

 discussion. In other words, an obvious classification of the snares 

 of the Orbitelaria3 does not correspond with a classification of the 

 species and genera according to their affinities as exemplified by 

 structure. As an illustration of this may be pointed out the fact 

 that within the limits of the genus Epeira Avebs of very different 

 types may be constructed. The commonest type is a simple, vertical, 

 full-orbed net with a meshed hub {sic) ; but in the species known as 

 Ep. labyrinthea a system of netted lines is associated with the ordi- 

 nary web ; in Ep. tnaranea the web is not full-orbed, but lacks one 

 sector ; the web of Ep. gihherosa is horizontal and not vertical ; 

 and, lastly, Ep. basilica weaves the remarkable net which Dr. 

 McCook has described as the domed-orb. On the other hand, the 

 •web of Gastracantlia is almost like the web of the ordinary type of 

 Epeira ; that of Zilla., not to mention Ncphila., resembles that of 

 triaranea in lacking a sector : that of Tetragnatha is like that of 

 (fibberosa in being horizontal. It appears, then, that there may be a 

 greater difference between the webs of a species of a genus than 

 between the webs of distinct genera ; thus the web oi Epeira basilica 

 is far more unlike the web of, e. g., Ej). diademata, than is the web 

 of Zilla or even Avfjiope. 



Since, then, the form of the web is liable to so much variation 

 within the limits of a single genus, and since species belonging to 

 different genera may spin snares that are almost exactly alike, it is 

 clear that great caution should be used in concluding that spiders 

 which make webs on a particular plan are necessarily related to 

 each other. But it is impossible to pursue this interesting topic 

 further. Enough has been said to give some idea of, perhaps, what 

 is one of the most important lessons to be learnt from Dr. McCook's 

 researches into the nature of webs. 



* For an able and exhaustive criticism of this classification reference 

 may be made to Dr. Thorell's paper in the Ann. & Mag. Nat. Hist, 

 vol. xvii. pp. 301-526 (1886). 



