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SILURIAN TRILOBITES. 



I have only lately obtained a good specimen, which is given in the woodcut ; and 

 ascertained that this Woolhope species is quite distinct from the H. delphinocephalus, 

 of which it was formerly thought a variety. 1 It is a far more convex species, and might 

 easily be mistaken for the H. Johannis, to which it is indeed nearly allied (we have 

 not the head as yet), and differs only, so far as I can see, in the want of trilobation, 

 more tapering body-axis, and rather longer pleuras ; but especially by the cylindrical convex 

 tail, with a much flatter axis, and less distinct side-ribs than in that species. The 



Fig. 27. 



Homalonotus cylhidricus ; Woolhope. (Mr. Edgell's cabinet.) 



differences in the tail are indeed so marked, that I cannot doubt its being a distinct 

 form, and it has probably been always quoted as If. delphinocephalus from Woolhope. 



Rather a large species. It must have been full 5^ inches long when perfect, and 

 2^ inches broad. The sides are very parallel as far as the root of the tail ; the outline 

 thence curves rapidly inwards towards the end of the tail-axis, and is again much produced 

 into a straight and somewhat cylindrical point. The depth is very great for a Silurian 



1 //. cylindricus is probably the common Woolhope species. It is now distinguished for the first 



time. 



