ANATOMY AND RELATIONS OF THE EURYPTERID^E. 517 



may very likely be a more primitive form than the ordinary one ; and if it be so, it 

 would point to the bilobate telson as the original type. 



The metastoma has the same position and relations as in Slimonia, but is broader in 

 proportion to its length, agreeing in this respect with the broader form of the carapace. 



The genital operculum has fundamentally the same structure as in Slimonia, but the 

 median lobe never shows such elaboration. It appears in two chief forms ; but as most 

 of the specimens in which it can be made out are too fragmentary to be specifically 

 determined, it is impossible to say whether the difference is merely sexual or not. The 

 short form of the central lobe is shown in fig. 13, which probably belongs to Pt. bilobus. 

 It is very short and broad, and the plates are also broad in proportion to their length. 

 The other type (fig. 14) is long and narrow, with a ridge down the middle and ending in 

 a triangular point. This form is found with Pt. bilobus, and in one case (fig. 14) is 

 associated with an unusually large second abdominal tergite, which suggests that it apper- 

 tained to a female. 



The series of branchial lamellae underlying the genital operculum has been figured by 

 Woodward,* and I have been unable to add anything of importance to his description. 

 Fig. 14 is part of the specimen which he figures, and shows these lamellae. Whether 

 there was a plate-like appendage behind the genital operculum, as in Slimonia, is not 

 quite certain. Pohlmann t figures what appears to be one in Pt. Buffaloensis, and the 

 specimen, which shows the branchial lamellae (fig. 14), appears to have a second plate 

 lying partly over the genital operculum (ix). The presence or absence of appendages 

 on the succeeding segments is even more obscure. Schmidt figures a whole series in Pt. 

 osiliensis similar to those in Eurypterus Fischeri, but his figures do not seem to me quite 

 conclusive. He further denies the existence of abdominal sclerites ; a statement in which 

 I am unable to agree with him. 



I have not been able to fit in the appendages figured by Dr Woodward on p. 91, and 

 doubtfully referred by Salter to Pterygotus. They certainly appear to belong to some 

 member of the order, but do not resemble what is known of the abdominal appendages of 

 this or other forms. 



Eurypterus. 



There is less to be added to what is already known of Eurypterus than was the case 

 in the two preceding genera, partly because the specimens are as a rule less well preserved, 

 but chiefly because its anatomy has been so well described by Schmidt.^ My observa- 

 tions, therefore, will necessarily take the form of a criticism of some of the points 

 described by Schmidt, though, as I have not had an opportunity of examining the 

 magnificent collection in the Reval Museum, I feel that considerable caution is necessary 

 in this. 



The most conspicuous points in which Eurypterus differs from the two preceding 



* Loc. cit., pi. xii. fig. 1, d. t Bull. Buff. Soc. Nat. Sci,, vol. v. pi. iii. J Loc. cit., p. 73. 



VOL. XXXVII. PART II. (NO. 24). 4 I 



