20 PROCEEDINGS OP THE AMERICAN ACADEMY 



joints about twice as long as broad. Lengtli to end of abdomen 

 proper, 13.5 mm. Mazon Creek, 111. (R. D, Lacoe, No. 1754.) 

 Fuller description deferred. 



The discovery of this fossil is one of the most interesting in this 

 field in recent years, as it is the first of the Pedipalpi yet found in 

 paleozoic rocks, or perhaps in any deposits, and it differs from modern 

 types no more than do the carboniferous scorpions. It was brought 

 to my notice after the rest of this paper was in type. 



Order SCORPIONES Thorcll. 



In his paper in the Transactions of the Royal Society of Edinburgh, 

 where he added so much to our knowledge of fossil scorpions, Mr. 

 B. P. Peach remarks that, "although there seems to be sufficient reason 

 to separate the genus [Eoscorpius] from any recent one, these ancient 

 scorjiions appear not to differ in any essential character from those 

 now living"; and Dr. A. Geikie, in commenting on Mr. Peach's dis- 

 coveries in "Nature" (vol. xxv. pp. 1-3), says, "It is obvious that 

 the scorpion has remained with hardly any change since carboniferous 

 times." Geikie also notices that " the chief diflference between the 

 living scorpion and its ancient progenitors lies in the fact that in the 

 fossil forms the mesial eyes are much larger in proportion to the lateral 

 ones, and also to the size of the whole animal." 



There are, however, some points in the structure of these paleozoic 

 forms which show that they differ from modern types more than the 

 above statements would appear to warrant. In the only one of Mr. 

 Peach's figured specimens showing clearly the under surface of the 

 cephalothorax, we find that the coxfc of the second pair of legs do not 

 touch along the middle line of the body, as in all living forms, (where 

 they cut off anteriorly the so-called sternum,) but are separated by 

 a pair of independent plates — the sternites ajiparently of the second 

 thoracic segments — which lie in advance of the sternum proper. 



In addition to this, the structure of the comb, upon wliicli in part the 

 families of living scorpions are based, differ remarkably from all recent 

 forms, if we are to judge solely by the information Mr. Peach has 

 given us. In all living types the combs are made up (1st) of a variable 

 number of longitudinally disposed lamellae. These form an anterior 

 row, composed of two or three (generally three) plates, the basal much 

 the larger ; a posterior row of numerous minute rounded scales, and an 

 intermediate series more or less numerous, disposed in from one to 

 three longitudinal rows, of which the basal ones are the larger, and the 

 others generally larger than those of the posterior row, exce])ting 



