TRILOBITES OF THE UPPER SILURIAN ROCKS. 



65! 



TRILOBITES OF THE UPPER SILURIAN ROCKS, (LUDLOW AND WENLOCK 



FORMATIONS.) 



The prominent family distinction of Trilobites, is the division of their abdomen and post 

 abdomen into 3 longitudinal lobes, by two furrows ; which character being scarcely perceptible in 

 this remarkable genus, it has been named (by Mr. Konig) Homalonotus. 



Homalonotus. The following is the short account first given in " Icones Sectiles," No. 85, 

 from a mutilated specimen, of the distinctive characters of 

 Homalonotus Knightii, (Konig.), PI. 7- f« 1 and 2?. 



" Testa ovata (?) acuminata : pars anterior sive caput ? ; corpus multiarticular m, 



dorso piano (nec trilobo) ; pars postica s. cauda simplex, acuminata, parva. 

 " Nominis occasionem praebuit planities dorsi. 



" Exemplar hoc unicum insidens lapidis calcarii fragmini, in Herefordise Comitatu, non 

 vero in situ, ut ajunt, reperto, pro humanitate sua ad nos transmisit vir ornatissimus, Andreas 

 Knight, Soc, Hortor. Colendor. Prases." 



The above generic character was derived from a form very nearly resembling our figure PI. 7- f. 1 . 



Owing to the imperfect condition of the specimens, it is difficult to say whether the form 

 f. 2. belongs to the same species. 

 Homalonotus Ludensis, (N.S.) PI. 7- f- 3 & 4. 



Head ovate- acuminate? ornamented with small tubercles (f. 3.). Body imperfectly trilobed 

 by tivo slight longitudinal depressions marked with tubercular cavities, ribs 13 ? Caudal 

 portion (Pygidium) wbs 9 ? tail a plain prominent boss prolonged to a sharp point. 



I have ventured to separate this species from H. Knightii, Konig, on account of the longi- 

 tudinal depressions which almost divide the animal into 3 lobes. We have no means of deter- 

 mining the form of the head of Homalonotus Knightii, and we can merely refer to the draw- 

 ings to convey an approximate idea of that member in II. Ludensis ; for that of f. 4. is much 

 compressed, and that of f. 3. has been mutilated. In the general form of the caudal portion, 

 there is, indeed, no well-marked difference between //. Knightii and H. Ludensis ; and I have 

 ascertained from other specimens, that both species had pointed tails, like f. 4., the square 

 terminations of figs. 1, 2 and 3. being solely due to mutilation. 



Loc. The Homalonotus Knightii and II. Ludensis are very characteristic of the Ludlow 

 formation, and particularly of its upper division, in which fragments of them are found 

 throughout the Silurian Rocks of Salop, Hereford, Worcester, Radnor, Brecknock, &c. 



Fig. 1 . is drawn from a specimen discovered by the Rev. T. T. Lewis, near Ludlow. Fig. 2. belongs 

 to Mr. B. Bright, and is from the western flanks of the Malvern Hills. Figs. 3. and 4. are 

 from Ludlow. The former is in the Cabinet of Mr. Evans, Hon. Sec. Worcestershire Nat. Hist. 

 Soc. ; the latter was found by Mr. Edward Davis of Presteign. 



Homalonotus delphinocephalus, nob. {Trimerus delphinocephalus ?, Green), PI. 7 (bis) f. la, lb. 

 Head depressed, ovate-acuminate. Front of head approaching to even, anterior part flat, 

 slightly raised, and marked with indistinct protuberances. Posterior end marked by a deep 

 groove which produces a ridge closely resembling one of the body ribs. Eyes prominent, 

 rather small, papillary and truncated. Facial suture (linea facialis) curved, apparently 

 dividing the eye in ttvo, and separating the central lobe from the lateral lobes, passes within 

 the raised anterior margin. Body composed of 13 ribs ivith intercostal plates, which extend 



