528 MR MALCOLM LAURIE ON THE ANATOMY OF THE EURYPTERID^E. 



that it would be impossible to abolish it, though it expresses a stage in the evolution of 

 the group rather than a relationship of those forms in contradistinction to the rest of the 

 Arachnida. Walcott's proposal to use Merostomata for the Eurypterina alone, excluding 

 Limulus, seems to be carrying change of meaning rather far, as the name was invented 

 by Dana for Limulus. 



In a tabular form the arrangement would be — 

 Class Pascilopoda. 



Sub-class A, Trilobita. 

 Sub-class B, Arachnida. 

 Order i. Xiphosura. 

 ii. Scorpionina. 

 iii. Eurypteridse. 

 iv. Pedipalpi. 

 v. Aranese, &e. 



EXPLANATION OF PLATES. 

 Plate I. 



Fig. 1. Walking leg of Sliinonia, showing general form and epicoxite (epc) on. basal joint. 



Fig. 2. Second appendage of Slimonia, " Antenna " of Dr Woodward. 



Fig. 3. First appendage (chelicera) lying in front of mouth. x £. 



Fig. 4. Epistoma of Slimonia. 



Fig. 5. Ventral view of first few abdominal segts. of Slimonia, showing genital operculum (vii) ; branchial 

 lamellae of second segment (viii) ; and plate-like appendages, with underlying branchial larnelke, of third seg- 

 ment (ix). x L From a specimen in the Woodwardian Museum. 



Fig. 6. Series of branchial lamellae, probably belonging to the second abdominal segment. From a speci- 

 men in the collection of Dr Hunter of Braidwood. x J. 



Fig. 7. Plate-like appendage with branchial lamellae of one of the posterior abdominal segments, probably 

 the fifth. From a specimen in the Jermyn Street Museum. 



Plate II. 



Fig. 8. Ventral body-wall of abdomen seen from inside, and showing branchial lamella? on segments xi. 

 and xii. x L From a specimen in the British Museum. 



Fig. 9. Restoration of Slimonia from the ventral surface. 



Fig. 10. Pterygotus. Epistoma, from a specimen in the Woodwardian Museum. 



Fig. 11. One of the walking legs of Pterygotus. epc, epicoxite. 



Fig. 12. A leg of Limulus showing the epicoxite. 



Fig. 13. Genital plate (form a) of Pterygotus. 



Fig. 14. Pterygotus bilobus, showing genital plate (form /?). A second plate-like structure (? ix), some 

 branchial lamellae, &c. From a specimen in the Jermyn Street Museum. 



Fig. 15. Thelyphonus. Ventral surface, for comparison with fig. 9. Ge.a., genital aperture. LB 1 and 

 LB 2, first and second lung-books of left side. 



10 F£3.94 





