EURYPTERUS LINEARIS. 147 



belong to the opposite sex, as the individuals are nearly of the same size, and occur in the 

 same strata, namely the passage-shales between the Upper Ludlow Rock and the Old Red 

 Sandstone, in the Ludlow railway-cutting. 



" Telson expanded and cordate at base, the broadest portion being less distant from 

 the insertion than one third the entire breadth. From thence the tail-joint is regularly 

 acuminated, the length being only two and a half times the breadth. The edge is crenato- 

 serrate like the last. We have only the flat under surface." 



Locality. — Ludlow, associated with Stylonurus (Eurypterus) megalops and other forms 

 of Eurypterida. 



Species 5.— EURYPTERUS LINEARIS —Salter. PI. XXVIII, figs. 10, 11, 12. 



Eurypterus linearis, Salter. Quart. Journ. Geol. Soc, 1859, vol. xv, p. 234, pi. x, 

 figs. 15, 16 a and b. 



Of this form Mr. Salter writes — " As this occurs generally in a lower stratum (Upper 

 Ludlow Rock) than E. acuminatus, it is little likely to have any relation to that species, 

 though the differences are such as might be due to sex. If, however, E. megalops and E. 

 acuminatus be one species, E. linearis must rank as distinct. The telson, the only part 

 preserved, is greatly more elongated than in the other forms. 



" Telson linear, lanceolate, nearly five times as long as wide ; the base very little 

 expanded, broadest near the point of insertion, or rather parallel-sided for a short distance, 

 and then attenuated. A strong median carina runs the whole length, elevated into a 

 steep ridge near the origin of the joint, and the edge is so faintly crenate as to appear 

 smooth to the naked eye." 



Fig. 10 "shows a broader telson, from the same bed, and it most probably bears the 

 same relation to E. linearis that the last-described species does to E. [Stylonurus] megalops. 

 From analogy we must suppose the broader tail-joint to belong to the female, and the 

 narrower one to the male." 1 



1 The only " analogy " which I can suppose was present in Mr. Salter's mind, in reference to the 

 expanded form of the telson in Eurypterus being indicative of the female and the narrower one of the 

 male, will, I fear, if followed, lead to error. 



I can, of course, only infer, but it seems very probable, that Mr. Salter's observation had reference to 

 the abdominal segments in the modern Brachyura, in which the female crab has a broadly expanded 

 abdomen, and the male an exceedingly narrow one. 



But as this diversity in form has a direct relation to the office performed by the caudal segments, 

 whether in the female crab, lobster, or prawn, namely, the convoy and protection of the eggs after extru- 

 sion from the ovaries and before hatching, we can hardly imagine a part not fulfilling such offices to 

 be so modified. As stated elsewhere (see ante pp. 109 and 110, and pp. 114 — 118) it, is the antennce 

 and the opercular plate which in this group of Crustacea undergo important sexual modifications. I 

 consider that the form of the telson is of great value as a specific character. 



