Notes on Sjjecies of Ceratiocaris. 387 



1. Ceratiocaris Murchisoni (Agassiz), and its variety lepto- 

 DACTYLUS (M'Coy). 



Some imperfect caudal appendages or spines (telson or style, 

 and lateral spines or stylets), from the Ujjpermost Ludlow strata, 

 near Ludlow, were figured in Murchison's Silurian System, in 

 1839, as fish-defences. These were recognized by Prof. F. M'Coy 

 in 1853 as being very similar to some analogous fossils, referred by 

 him at first (in 1849) to a slender-clawed kind of Pterygotus from 

 the Lower Ludlow, at Leintwardine, near Ludlow, which he separated 

 from that genus as Leptocheles leptodactylus. M'Coy suggested that 

 Murchison's fossil should be known as L. MurcJiisoni} 



In each case we have only caudal spines to deal with ; but M'Coy's 

 specimens (Brit. Pal. Foss. pi. 1 E, figs. 7, la, lb) are much 

 more slender than Murchison's (Sil. Syst. pi. 4, figs. 10 and 64, 

 and Siluria, pi. 1 E, figs. 1, 2), and less strongly ribbed; and 

 therein they seem at first sight to have specific differences. 



Several good examples of more or less perfect sets of the three 

 caudal spines corresponding in size, strength, and ribbing, with 

 Murchison's fossils have been met with. These show evidence of 

 lines of prickles (by the presence of little pits, representing their 

 bases, along one or more lines) ; and on close examination the en- 

 gravings in the Sil. Syst. and Siluria (the specimens have 

 been lost) show some slight indications of this spinose ornament. 

 This is not visible, however, in M'Coy's figures or specimens 

 (Cambridge Museum, a/923, a/924). Of these latter, more delicate, 

 caudal appendages, very few other examples occur. 



In the collocation of these caudal appendages with their respective 

 carapaces we have some doubt and difficulty. 



We have not found a carapace directly associated with any com- 

 plete spines of either the Murchisoni ov leptodactylus type except in the 

 case of a very small specimen (M. P. G. x ^), which appears to have 

 the caudal appendages of C. MurcJiisoni and the carapace of Salter's 

 " leptodactylus.''^ With regard to both, however, the late Mr. J. W. 

 Salter satisfied himself that he knew their special carapaces, for he 

 described them at p. 157 of the Ann. Mag. Nat. Hist, for March, 

 1860 : where also he refers both species to the Ceratiocaris of M'Coy. 

 Judging from his Latin diagnoses, he allocates to the former — " a 

 cephalothorax (carapace) two inches long, oblong, convex, orna- 

 mented with interrupted, nearly-straight, wide-apart lines. The 

 caudal appendages long, sub-cylindrical ; the centre spine (telson) 

 strong, bulbous at its base, and with a strong dorsal rib ; the side 

 spines long. All ribbed. The whole animal medium-sized. Speci- 

 mens possessed by the geologists at Ludlow and by the Museum of 

 Practical Geology." The carapace described here does not agree 



1 Prof. M'Coy's observations are as follows : — " . . . As before mentioned, figs. 

 9, 10, and 11 [Sil. Syst. pi. 4; omit figs. 9 and 11], representing the so-called 

 Oiwhus Murchisoni, Ag., are almost identical in form, size, sculpturing, and all 

 other characters (as far as they are represented in these drawings), with the distinctly 

 didactyle pincers which I have figured (Brit. Pal. Foss. pi. E, "fig. 7) from Leintwar- 

 dine, under the name Lept. leptodactylus. ... If this approximation prove correct, 

 the fossil should in future be called Leptocheles Murchisoni (Ag. sp.)."— Q. J. G. S. 

 vol. ix. 1853, p. 13. 



