70 SILURIAN TRILOBITES. 



Homfray, Esq.). Mr. Frederic Ash, formerly of Portmadoe, contributed many specimens 

 of Tremadoc fossils to the Museum of Pract. Geology ; and the species is named after 

 him, to record his labours in the district. 



Sph^erexochus, Bey rich. 



Eyes facetted minutely ; head very convex, almost globular; the cheeks not scrobiculat.e ; 

 facial suture ending on the external margin, near the angles, in front continuous and sub- 

 marginal ; glabella large and nearly spherical, with three furrows on each side, the two 

 upper very obscure, the lower strong and curved down to the neck-furrow ; thorax of 

 eleven joints, without any furrows ; tail of three segments, free at their ends ; labrum 

 subtrigonal, with a marginal furrow, but without lateral farrows. No rostral shield. 



As the labrum of the last described section of Cheirurus, viz., Actinopeltis, has a very 

 similar labrum, it might be difficult to say in what, except in proportion, and in the 

 extreme convexity of all the parts, this very abnormal Trilobite differs from that subgenus. 

 However, as Sphgerexochus is widely recognised, and as, moreover, there appears to be no 

 rostral shield (that of Cheirurus is well established by Barrande), it is convenient to adopt 

 the name. 



Sph^rexochus mirus, Bei/rich. PI. VII, figs. 1 —6. 



Calymene clavifrons, Hisinger. Leth. Suec, 2nd Supp., t. xxxvii, fig. 1, 1840. 

 Sph^;rexociiu8 mirus, Beyrich. Ueber einige Bohni. Tril., p. 21, 1845. 



— — Id. Zweite Stuck, t. i, fig. 8, 1846. 



— calvus, M'Coy. Syn. Sil. Foss. Ireland, pi. 4, fig. 10, 1846. 



— mirus, Corda. Prodom. einer Monog. Bohm. Tril., fig. 72, 184". 



— — Barrande. Syst. Sil. de Boheme, vol. i, pi. xlii, figs. 11, 18, 



1853. 



— — Salter. Decades Geol. Surr. No. 7, pi. iii, 1853. 



— — Id. Morris's Catal. 2nd ed., p. 115, 1854. 



A few years ago this was one of our rare British Trilobites. Now, the accident of a 

 tunnel being driven through the rich formations of the Malvern Hills has rendered it one 

 of the most frequent ornaments of the cabinet. Messrs. Gray and Fletcher obtained the 

 species first from the Dudley Limestone. Sir R. Griffith found it in the Caradoc Lime- 

 stone of Kildare, and Prof. M'Coy published it almost immediately after Beynch's 

 description had appeared in 1846. The Geological Survey collected it in abundance from 

 the same locality in Ireland; and now our friends, Dr. Griudrod, of Malvern ; Messrs. 

 Hollier and Ketley, of Dudley ; and Messrs. Allport, of Birmingham, have contributed 

 excellent materials, which enable us to complete the account. 



