234 On the rt Seraphim " and its Allies. 



the antennulcs of higher Crustacea ; the second pair (A 2) are 

 much larger, but chelate like the first; these aro the ant&n/nce, 

 their bases serving as palpi, or foot-jaws. These and the 

 three succeeding pairs of organs (A 3, 4, and 5) are alike in the 

 female Limulus, but in the male the antennas are peculiarly 

 modified (woodcut, Fig. C) — a sexual distinction found also to 

 exist in many other living Crustacea. 



I have thus minutely described Limulus because of its 

 affinity to Ptorygotus, and to its fossil congener Eurypterus ; 

 and now that we are enabled to give a correct restoration of 

 P. acuminatus (see woodcut, Fig. K), its relation to the living 

 form is still more clearly seen. 



Having fully satisfied myself as to the general homologies 

 that existed between the nature and position of the organs of 

 the living Limulus and scorpion, and the extinct Ev/rypterida, 

 especially as to the identity of the thoracic appendage already 

 referred to, my satisfaction was very much increased on subse- 

 quently finding that, in 1859, Professors Hall and Agassiz in 

 America, and, some years since, Mr. Robert Slimon in Scotland, 

 had each independently arrived at the same conclusion, from 

 the study of widely different specimens of the same fossil group. 



Mr. Hall writes (p. 394*), "Professor Agassiz regards the 

 central organ attached to the lower side of the first segment as 

 similar to the appendage attached to the membranous feet 

 behind the swimming feet of Limulus (see woodcut, Fig. B) ; 

 and, instead of being double, is anchylosed as in young Limu- 

 lus. Since my comparisons had been made almost entirely 

 with Limulus, I am prepared to appreciate these views of Pro- 

 fessor Agassiz." 



Mr. Slimon writes me, "It is a number of years since I 

 found that plate (see frontispiece,/, cj, and woodcut, Fig. K m), 

 but it being detached I could form no conception of what it 

 was, and many palaeontologists who saw it were equally at 

 a loss to explain its nature. At last I found one in situ, which 

 threw some light on the subject ; still its use remained a 

 mystery. After some time I obtained the other kind of plate 

 (see woodcut, Fig. E), attached to an individual of the samo 

 species (P. acuminatus) . This led me to the conclusion that it 

 w;is connected with the sexual organs, and that one form 

 of plate would indicate the male and the other the female. 

 Lately I have observed something like eggs (Fig. F) lying near 

 plate E)j so, probably, this may prove to be tho female." * * 



* Sec Geological Surveyof X< w York, vol.iii., "Paleontology," 1859, by James 

 Hall, Ifiaq. On the genua "Eurypterus, pp. 892 — 418; Doliohopterue, pp. 414, 

 415; and Pten/gotut, pp. 416— 419. Plates 80, and nine following plates, and 

 plate 84 a. Brom which tho figure of the head of Swypterut (restored) is 

 copied (woodcut, Pig. G). 



