i893. EURYPTERIDA. 127 



As regards the zoological position of the Eurypterids, the esta- 

 blishment of the number of cephalothoracic appendages as six, the 

 first pair being pre-oral and — at all events, in most forms — chelicerae, 

 seems to considerably strengthen the argument for their relationship 

 to the Arachnida. The presence of abdominal appendages also 

 makes them agree much more closely than before with Linmlus, and, 

 if the lung-books are to be derived from such appendages, with 

 Scorpio, &c. It has been pointed out, however, (6) that the great 

 development of the genital operculum and consequent partial sup- 

 pression of the second free segment is a point of some morphological 

 importance, and contrasts strongly with the development of the same 

 parts in Limulus, and even more strikingly in Scorpio. On the other 

 hand, it agrees very closely with the arrangement in the Pedipalpi, in 

 which a similar suppression of the second segment has taken place, 

 and it seems probable that these latter are more nearly allied to the 

 Eurypterids than are the Scorpions. This view would tend to 

 separate Glyptoscorpius somewhat from the Eurypterids, but as the 

 only evidence of relationship is the presence of scale-markings which are 

 common to many other forms (Trilobites, Phalangidae, etc.), there can 

 be no serious objection to this. The relationship of these forms to the 

 Crustacea is not so evident, as they show no special points of affinity 

 with any one group. The absence of that special modification of 

 three pairs of appendages to serve as mouth organs, which is 

 characteristic of all Crustacea except the Ostracoda, indicates that 

 their point of union must have been very low down the Crustacean 

 stem, and the very definite number of segments and arrangement 

 of appendages in the Eurypteridae indicates on the other band 

 that they are removed a considerable distance from any such primitive 

 type. Insofar as they are somewhat more primitive forms than the 

 recent terrestrial Arachnids, they may undoubtedly be said to be 

 nearer to the point of union of the Crustacean and Arachnid lines of 

 descent, but, unless great, and, it seems to me, undue importance is to 

 be attached to their aquatic mode of life, they can hardly be termed 



intermediate forms. 



REFERENCES. 



1. Huxley and Salter. — Anatomy and Affinities of Pterygotus. Mem.Geol. Siirv. 



Monograph i., 1859. 



2. Hall, J. — Natural History of New York. Palaeontology, vol. iii. 



3. Woodward, H. — British Fossil Merostomata. Man. Palaontographical Soc, 



1866 -1878. 



4. Schmidt, F. — Die Crustaceenfauna d. Eurypterusschichten v. Rootzikiill. 



Mem. Acad. Imp. Sci. St. Petevsboiirg, vol. xxxi., 1883. 



5. Hall, James. — 2nd Geol. Surv. Pennsylvania. Vol. P. P. P., 1884. 



6. Laurie, M.— Anatomy and Relations of Eurypterida. Trans. Roy. Soc. Edinb., 



vol. xxxviii., 1893. 



7. Peach) B. N. — Crustacea and Arachnida of the Carboniferous Rocks. Trans. 



Roy. S0C. Edinb., vol. xxx., 1881. 



8. Laurie, M. — Some Eurypterid Remains from the Pentland Hills. Trans. Roy. 



Soc. Edinb., vol. xxxvii., 1892. 



Malcolm Laurie. 



