TRILOBITES OF THE LOWER SILURIAN ROCKS. 



663 



because the central abdominal lobe in each seems to bear precisely the same relative proportions 

 to the flanks or sides of the animal, and to exhibit the same sudden contraction towards the tail. 



The large specimen, PL 24., presented to me by the Earl of Cawdor, must, however, be con- 

 sidered a variety on account of its ornamented surface 5 and I have therefore named it Asaphus 

 tyrannus, var. ornata. Although merely a hollow impression, which has been long exposed 

 action of the weather, it gives a clear idea of the general form and size of the animal, which 

 was nearly one foot in length. 



The Asaphus tyrannus is equally abundant with the A. Buchii in the Llandeilo flags of 

 Caermarthenshire and Pembrokeshire (pp. 357, 397). It is usually found without the head, 

 as in PI. 25. f. %.* but even in that condition, the observer can never fail to distinguish it by 

 the great width of its central lobe and the pointed tail, which is strongly contrasted with the 

 round termination of A. Buchii. The latter is of smaller size j the largest specimen I have 

 ever seen not exceeding five inches in length, while the new species is often six or seven inches 

 long. This circumstance induced me to give it the name of tyrannus, in order to mark this 

 species as the chief being of his race, during the period when the Lower Silurian Rocks were 

 accumulating. 



The noble specimen A. tyrannus, var. ornata, is now placed in the British Museum, illus- 

 trated by casts taken from the intaglio figured. It does not appear that any writer has alluded 

 to a specimen of this magnitude ; but Professor Phillips informs me, that in a recent tour in 

 Norway he sketched the outline of one in the rock, of about the same size, and apparently of 

 the same species. 



Loc. Banks of the Toivy, near Llandeilo ; and in Dynevawr Park and Golden Grove; 

 Clog-y-frain, near St. Clears, Caermarthenshire ; Llampeter felfrey, Pembrokeshire. 

 Asaphus Corndensis, (n. s.), PL 25. f. 4. 



This species approaches near to Asaphus Buchii, Brong., but is distinguished from it by 

 the greater length of the lateral spinose terminations of the buckler, which advance poste- 

 riorly to the penultimate or seventh rib of the body, and also by their terminating obtusely. 

 Loc. Found by myself in dark-coloured flagstone, alternating with volcanic grits, near Middle- 

 ton, on the north-ivestern Jlank of the, Corndon Mountain. I have named it after the 

 dominant feature in a tract so interesting from its varied geological phsenomena. (See 

 Chapter 22.) The same fossil is associated with Asaphus Buchii, A. tyrannus, and other 

 species too imperfect to be named, at Rorrington and Meadowtown, in the north-north- 

 eastern prolongation of the same band of Llandeilo flags, and also in the undulating strata 

 of the same age in the adjacent mining tract of Shelve, Hope Mill, &c. 

 Asaphus? Vulcani, n. s. PL 25. f. 5. 



Head ptmrn, the central division being cuneiform at the front, and truncated at the anterior 

 margin. Central lobe of caudal portion contracted in the middle. 



Loc. This specimen, with others too imperfect to describe, was found coiled up in the volcanic 

 grit on the western flank of the Corndon Mountain above alluded to, in a ravine east of 

 Middleton. I have, therefore, so named the fossil, that its discovery may be connected 

 with the supposed origin of the rock in which it was imbedded. (See Chapter 22, p. 270.) 

 The same species is found in the Caradoc formation near Wistanstow, associated with 

 Asaphus PowisiL 

 Ogygia, Brongniart, 



Gen. Char. — Corps tres deprime, en ellipse allongee, non contractile en sphere. Boucher 



4 p 2 



