74-G SCIENTIFIC Rl'CORD FOR ISSr). 



with the Silurian) the most important, the expectant ground of the stu- 

 dent of palaBontology. 



It would then appear that the geological history of winged insects, so 

 far as we know from present indications, may be summed up in a very 

 few words. Appearing in the Silurian period, insects continued through- 

 out Paleozoic times as a generalized form of Heteroniefahola, which, for 

 convenience, we have called Palceodictyoptera, and which had the front 

 wings as well as the hind wings membranous. 



On the advent of Mesozoic times a great differentiation took place, 

 and before its middle all the orders, both of Heterometahola and Metahola, 

 were fully developed in all their essential features as they exist to day; 

 the more highly organized Metabola at first in feeble numbers, but to-day, 

 aud even in Tertiary times, as the prevailing types. The Metabola have 

 from the first retained the membranous character of the front wings, 

 while in most of the Seterometahola, which were more closely and di- 

 rectly connected with Palaeozoic types, the front wings were, even in 

 Mesozoic times, more or less completely difierentiated from the hind 

 wings as a sort of protection covering to the latter, and these became 

 the principal organs of flight. 



ScuDDER, S. H. — (A Contribution to the Geological History of Myrio- 

 pods and Arachnids, in Psyche). Amer. Nat., vol. xix, pp. 1210, 1211. 

 December, 1885. Philadelphia. 



An abstract of Mr. Scudder's article in Psyche. 



The great Archipolypoda resemble the Diplopoda in having two pairs 

 of legs on every segment ; while in the Protosygnatha only a single pair 

 of legs is borne by each segment, and the group thus resembles the 

 Ghilopoda. For a brief period after leaving the e^g:,., modern diplopods 

 and pauropods have a shorter body than in after life, and the first three 

 segments bear but a single pair of legs. In adult life these first three 

 segments still bear but a single pair of limbs, while all the other seg- 

 ments, both those which exist in the larval state and those which de- 

 velop afterwards, bear two pairs. The Chilopoda have these same 

 anterior pairs of limbs early and permanently developed as organs of 

 manducation, while all other segments have but a single pair. Palseon- 

 tologic evidence is in favor of the view that the dorsal scutes of Diplo- 

 poda are compound. The archipolypodous type is the oldest, and there 

 is evidence that some of the Carboniferous forms were amphibious. The 

 group culminated in the Carboniferous, and does not appear to occur 

 later than the Dyas, while, with one doubtful exception, no true diplo- 

 pod is known to be older than the Oligocene. According to S. H. Scud- 

 der, between twenty and thirty species of pre-Tertiary Arachnida are 

 now known, and the earlier forms, chiefly of Carboniferous age, belong 

 either to the Scorpionides or to the Anthracomarti, a group which is 

 not known later than Palaeozoic times, the only Mesozoic arachnids yet 

 known being true spiders. 



