1859.] EGERTON — OLD RED FISHES. 131 



plate, m, and the arched dorsal plate, Z, there occurred two lateral 

 plates of considerable size, omitted by Agassiz, and which corre- 

 sponded to the two dorsal lateral plates of Pterichihys. It is a 

 curious circumstance, that both genera had the same number of 

 plates, eleven, in the cuirass which covered the body, — the Pterich- 

 thys having two central dorsal plates, and but one central abdominal 

 plate, and the Coccosteus but a single dorsal plate, and two central 

 abdominal ones. In both, too, the body impinged further on the 

 head ventrally than dorsally. The anterior end of the dorsal plate 

 of Coccosteus terminated nearly opposite the line z." 



Letter without date. 



" In the concluding part of my very rambling geological chapter 

 of to-day, you will find reference made to what I deem a new 

 species of Coccosteus, and in the enclosed little box the cast of one 

 of the best specimens of the species, or variety, yet found (fig. 3). 



Fig. 3.— Plates of Fig. 4.— Dorsal Plate of 



Coccosteus pusillus, M'Coy. Coccosteus pusillus, M'Coy. 



0fM 



p\ 



It shows, on at least two of the plates, the numerous tubercles, vary- 

 ing from microscopic to minute, on which I have ventured to challenge 

 for it a specific status, and also the eye-hollows referred to in my 

 description, but not those lines of increment which I also found. 

 These, however, are very apparent on the cast of the single dorsal 

 plate (fig. I) which accompanies it, and which, tor this species, is 

 large. l!\ letting the light fall slantwise on this latter cast, yon 

 will see the plate reduced by line within line till, at length, in tho 

 centre it appears as a miniature thing, little more than half an inch 

 in length by about the eighth part of an inch in breadth. In tho 

 cast of the more perfect specimen, there is a slight distortion indi- 

 cated in this dorsal plate; but it seems to be merely the result of 

 BOme accident peculiar to the individual, and is not shown in any 



of the other specimens, I purpose in my next chapter attempting 

 a general description of Coccostetu, which, however, from the want 



of a print, cannot, I am afraid, l>e other than obscure." 

 vol.. xvi. — PART 1. 1. 



