NO. 14 



INSECT ABDOMEN SNODGRASS 



29 



preabclomen, since the extra segment of the scorpions appears to 

 be in this region of the body. Moreover, the last gill plates of 

 Xiphosura and the last lung books of the scorpion are on seg- 

 ment XIII, while the last gills of the eurypterids are said to be on 



2L iL Chi Pdp 



Chi (I) 



^Cxndj 

 -Cxnds 



Opi(vm) 



'IXS 

 -Pec 



-Eurypterida 



segmentation and external 



Fig. 10. 

 genitalia. 



A, diagram of an eurypterid, ventral view (from Clarke and Ruedemann, 1912). 

 B, reconstruction of Mixoptertis kioeri (outline from Stormer, 1934). C, same 

 dorsal view of prosoma and preabdomen. D, body of a scorpion, ventral view. 

 E, ventral parts of genital and postgenital segments of scorpion. 



Chi, chelicera; Cxnd, coxal endite ; Gtr, gonotreme (opening of genital cham- 

 ber) ; 1-XVIll, postoral somites; 1L-4L, legs; oap, opercular appendage; Opl, 

 operculum ; Pdp, pedipalp ; Pec, pecten ; pgj, postgenital fold ; Prsm, prosoma ; 

 Sp, respiratory orifice ; Tel, telson. 



segment XII. The partial suppression of the first opisthosomal seg- 

 ment is a feature common to Eurypterida and Arachnida. Consider- 

 ing, therefore, the general structure of the eurypterids, so far as it 

 is known, and in particular the arachnid type of their body division 

 into prosoma and opisthosoma, it seems clear that the Eurypterida 



