98 D)\ Ivor Thomas — Devonian Fossils from CornivaU. 



The eijes (PI. Ill, Tigs. 1, 2, 4), of -wliicli only the left one is pre- 

 served in the specimen, are placed upon narrow free checks, roughly 

 rectangular in shape and lying at the anterior extremity of the fixed 

 cheeks. The facets, which are fully developed, are arranged in a single 

 row on a narrow suh-crescentic ridge, making a small angle with the 

 border. They are five in number, circular, and slightly diminishing in 

 size in either direction from the central facet. There is a possible 

 trace of a terminal rudimentary sixth facet. 



Thorax. — The axis is well defined, convex, with sub-parallel margins, 

 and slightly tapering towards the pygidium. The bounding dorsal 

 furrows are broadly deep. The segments, some of which are not 

 preserved, are slightly tuberculate at the sides. The jileura are 

 flattened and abruptly deflected backwards and downwards at the 

 fulcrum about two-thirds their width from the axial furrows, and are 

 grooved from the axis outwards, the anterior segment overlapping at 

 the deflected portion. 



The pygidium (PI. Ill, Fig. 3) is small in proportion to thorax. 

 The length to breadth = 2 : 5. The axis is prominent, convex, 

 and gradually tapering to a blunt end posteriorly. The number of 

 annulations is about six, and they become more weakly marked and 

 obsolete towards the posterior extremity. The pleura are slightly 

 flattened. The annulations are broadly rounded, faintly grooved, and 

 curved slightly backwards. A marginal border is not developed. 



Dimensions. — The length of the head-shield = 2'2mm. ; the breadth 

 of the head-shield = 3 '3 mm. ; the greatest breadth of the thorax 

 = 3*1 mm.; the length of the pygidium = O'Smm. ; the breadth of 

 the pygidium = 2'Omm. 



Locality and horizon. — One very small rolled-up specimen of this 

 Trilobite was found in a band of highly fossiliferous grey slates, 

 probably under 20 feet in thickness, exposed between the tide-marks 

 on the east side of Portquin Harbour and not far from the beach. It 

 is preserved in iron pyrites, and occurs together with a good assemblage 

 of small mollusca, similarly preserved : Tornoceras sim])lex ? (v. Buch), 

 Torn, vernenili (Miinst.), Torn. cf. suhmdulatum, Prech, forms near 

 to Torn, qlohosum (Miinst.) and Torn, planilolum (G. & F. Sandb.), 

 Orthoceras sp. ; small Gasteropods, Naticopsis spp., Platyostoma sp., 

 Bellerophon {Ptomaiis ?) sp. ; a few Lamellibranchs, Buchiola retro- 

 striata ? (v. Buch), and Allorisma condnna, sp. nov. A fragment of a 

 Trilobite showing a part of the thorax and pygidium occurs also in the 

 material; it probably belongs to the same species as the one described. 



The assemblage of Cephalopods points to an undoubted Upper 

 Devonian age, while the occurrence of forms near to lornoceras plani- 

 lolum, Torn, vernenili, and Torn, glohosum, which, with others, have been 

 placed by Professor Freeh (6,^ p. 125 ; la, p. 67) under a new genus, 

 Cheiloceras, appears to support a middle Upper Devonian horizon. This 

 Cheiloceras horizon was first noticed near Brilon by Professor Kayser 

 (11,^ pp. 602ff.), who named the beds " Nehdener'Schiefer ". They 

 lie at the base of the Clymenien-Kalk and are rich in Goniatites 

 jDreserved in iron pyrites. The same definite horizon has been 

 recognized by various investigators at Elsterburg in Thuringia, 

 ^ These figures refer to Bibliography at end of paper. 



