BRITISH FOSSILS. 3 



to the glabella and caudal axis. The front is constantly produced, the 

 surface minutely scabrous, not covered with scattered tubercles, but this 

 last character occurs in some varieties of C. Blumenbachii, which is 

 more variable than we formerly believed. 



Affinities. It is distinguished from C. Blumenbachii, with which it 

 has always been confounded, and to which it is closely allied, by the 

 broad depressed form, narrow axis,* glabella not higher than the cheeks, 

 distant fulcrum, and wide depressed tail ; the produced recurved snout 

 also is a strong character. C. brevicapitata has the snout recurved, but it 

 is shorter ; the axis is prominent, and the fulcrum close to it ; the glabella 

 also is much shorter and smaller in front, and the whole form is elongate 

 and cylindrical. With the American species, as published by Green, 

 Hall, and Emmons, it does not need a close comparison : C. senaria is 

 attenuated posteriorly, and has a wide head, close fulcrum, and a small 

 tail, with the axis as broad as the sides : C. callicephala is distinguished 

 at once by the very short triangular glabella ; it has also a close fulcrum. 

 It is quite possible that hereafter forms may be found which will con- 

 nect this species with the more common C. Blumenbachii ; but at pre- 

 sent we do not know such forms, and it is necessary to point out the 

 obvious characters which distinguish them. Between C. Blumenbachii, 

 however, and the other British species, C. brevicapitata, specimens 

 intermediate in character, both as regards form and sculpture, liave 

 been discovered ; the present species, therefore, being founded on some- 

 what similar kinds of variation, must be received with caution. 



History. The early figures and descriptions of animals of this genus 

 had, of course, no reference to such minute differences as are now 

 deemed necessary for specific character ; however, there is one early 

 figure which certainly resembles more the depressed tail of our spe- 

 cies, with widely spreading and curved side ribs, than C. Blumenbachii ; 

 we mean that of Linnceus, "Stockholm Trans.," 1759, t. 1, f. 3. 



Dalman describes, under C. Blumenbachii, three forms,t viz. : 



1. Var. tuberculata, in which he erroneously counts 12 segments to the 

 thorax, and reckons about seven ribs to the tail. Length, 2 inches to 2. 

 Gottland and England ; the English specimen having the axis of the thorax 

 tuberculate on the sides, as in the next variety. 



2. Var. Blumenbachii vera? a. tuberculosa, with 13 segments, and tail 

 with about eight ribs, the axis tuberculated on its sides ; the head, tail, and 

 lateral knobs of the axis closely scabrous; the dorsum (axis itself) smooth. 

 Length about an inch. Gottland. 



* There is a variety of C. Blumenbachii, with narrower axis, found at the Hollies, near 

 Horderley, but the glabella and tail are normal, and the front not produced. 



f " Et descriptiones auctorum, et specimina ad hac speciem relata, taiitas prcebent dis- 

 crepantias, ut fere credam diversas species sub hoc nomine esse commixtas, de qua re 

 tamen, ob speciminum inopiam, dijudicare nequeo." Dalman, Palaead., p. 35. 



