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SILURIAN TRILOBITES. 



basalibus tumidis. From 1 concava, subacuta, scitto rostrali quam lato longiori. Genes 

 convex <b : ocirfis ante medium positis. Thorax bene lobatus, granulis posticis spinoso- 

 pectinatis. Cauda triangularis convexa acuminata ; axe prominente 12-annuIato, lateribus 

 declivibus S-sulcatis, sulcis profundioribus. 



With great pleasure I recognised this new form in the very choice cabinet of my 

 friend John Lee, Esq., of Caerleon, and beg to dedicate it to him. It seems not to be 

 a rare species ; but has hitherto been confounded with the H. delphinocephalus, from 

 which it differs in every particular. More strongly trilobed, more roughly tubercular, 

 with a more triangular and far more deeply lobed head, a narrower tail-axis, and deeply 

 sulcate side-lobes to the tail, it is rather surprising the species had not attracted atten- 

 tion before. 



The length of large specimens is just 6 inches, the base of the head, which is the 

 widest part, being there 3^ inches. This gives a size all but equal to the great species 

 just described. The head itself is trigonal, 3^ inches wide at base, and 2 5 long, with 

 a blunt-pointed front and similar posterior angles. A broad neck-segment is deeply 

 divided from the tumid four-sided glabella, and these taken together are rather longer 

 than the concave front. The glabella is twice as wide behind as in front, trapezoidal in 

 shape, the angles rounded, the sides tumid, and the lateral lobes very distinct for the 

 genus ; the centre is raised and somewhat carinate, as in its ally II. delphinocephalus, but 

 the glabella is greatly wider behind. A distinct, wide, and rather strong sulcus borders 

 it all round, separating the tumid cheeks with their sub-central eyes. The course of the 

 facial suture is the same as in the last species. One specimen (fig. 2) shows the rostral 

 shield ; it is longer than broad, and is of a nearly rectangular shape. The whole head is 

 covered with a coarse and fine granulation ; but, as we have only internal casts, we cannot 

 give further details. 



Thorax depressed ; the rings convex, well separated from each other, and projecting 

 posteriorly more than usual ; the hinder half large, the anterior portion separated by the 

 pleural groove narrow, as in H. delphinocephalus. The trilobation is distinctly marked ; 

 the axis thus marked out being narrower, and more tapering backwards, than in the last- 

 mentioned species. Internally the pleural groove is very strong (see fig. 6). The pleura? 

 are square at their ends (fig. 5). 



The tail is strongly ribbed. The axis, not much broader than the sides, is tapering, 

 long-conical, and distinctly ribbed all down by nine strong ribs, while the sides have 

 seven strong furrows. The axis is prominent and pyramidal at their tip, and does not 

 fade off into the broad-pointed mucro, which is more than one third the whole length 

 of the tail, acute, not recurved ; it is much longer than in the allied species so often 

 quoted. 



1 I use the term frons for the produced front of the head, in front of the glabella. Some authors use 

 it for the glabella: — it is best to keep the terms distinct. 



