BRITISH FOSSILS. 



3 



not often aeen in those genera in which the faculty of rolling up is 

 lost or very limited. 



The tail is more pointed than a semicircle, the axis not as broad 

 as the sides, with two distinct rings, and a bluntish terminal por- 

 tion not reaching the tip. The sides are marked by two lateral 

 furrows which just reach the margin, opposite to the two short 

 lateral spines. The upper furrows are duplicated. The incurved 

 under margin * is very narrow, but convex. 



The compressed and elongated specimens (figs. 8, 4) were formerly 

 considered to be of a distinct species, not, however, on account of 

 the form, which I was aware might be due in great part to pressure, 

 but on account of the spinose border to the tail, a character I had 

 not at the time seen in figs. 1 and 2. A noble series of specimens, 

 distorted in every possible way, have been lately transmitted 

 by Mr. D. Homfray, of Portmadoc, who has collected the fossils 

 of that district with much success. 



These specimens show 15 segments (our figured specimens only 

 showed 14), and they prove clearly that the spinose border to the tail 

 occurs in all well-preserved specimens, yet in some more distinctly 

 than others. And the great difference in appearance between figs. 2 

 and 3 is entirely due to the different direction in which the fossils 

 have been pressed in the stone. The pleural grooves in the one case 

 are all but obliterated (fig. 3), in the other they are deepened (fig. 2), 

 and the spinose border to the tail (in fig. 3) appears to be increased in 

 length; in fig. 2 it is reduced. The somewhat greater space in front 

 of the glabella, and the long head spines in fig. 8, are differences 

 which may possibly (if the}^ be found constant) be referable to sex. 



Locality and Geological Position. — Upper Beds of the Tre- 

 MADOC Slates, Garth Hill, east side of Traeth Bach, Tremadoc, 

 N. Wales ; also Portmadoc Quarries, and at the Ynys Tywyn, in 

 similar beds. (Mus. Pract. GeoL, and cabinets of Messrs. Homfray, 

 F. Ash, and Mr. E. Roberts, surgeon, and many other collections.) 



Genus— C ONOCORYPHE. 



It is not usual to include more than one genus in a plate ; but 

 accident having introduced a Conocoryphe upon the plate of 



* We want a term for this incurved striated under margin, which is always more 

 distinct in the tail than elsewhere. Being always or most generally parallel- sided in the 

 tail, it might conveniently be termed the " caudal fascia in the pleurae, the "pleural 

 fascia," but the term is hardly necessary for any portion but the tail, where the relative 

 width of the fascia is of specific importance. 



11 G 2 



