92 BRITISH PALEOZOIC PHYLLOCARIDA. 



2. Caetocakis Mareii, Hicks, 1876. Plate XIV, figs. 16—18. 



Caetocaeis Maeeii, Hicks. Quart. Journ. Geol. Soc, vol. xxxii, p. 138. 



— — S. Woodward. Catal. Brit. Foss. Crust., 1877, p. 70. 



— — T.B. J. Geol. Mag., 1883, p. 464. 



— —T.B. J. and H. W. Eeport Brit. Assoc, for 1883 (1884), 



pp. 215 and 222. 



— Maeei[eeii], Woods. Catal. Type Fossils Cambridge, 1891, p. 134. 



Much like G. Wrightii in general appearance, but smaller, being both shorter 

 and narrower ; nearly straight on dorsal and ventral margins, but sometimes 

 slightly curved (PI. XIV, figs. 16 and 18), probably from the effect of pressure. 

 One end narrower and less decidedly truncate than others (fig. 17), and sometimes 

 rounded (figs. 16 and 18), having been modified by pressure. A good specimen 

 (fig. 17) is black, shining, and somewhat leech-like. 



In the Woodwardian Museum, Cambridge, some specimens from the Upper 

 Arenig schists on the Nantlle tramway are labelled G. Marrii, Hicks. 1. One, 

 with a black test, compressed, measures -rs 'X ^ inch, or 15 X 75 mm. ; and 

 this has been so much squeezed that possibly it is now even narrower than it 

 originally was ; but the front end is broken, and the hinder end is fringed off with 

 the " plaiting " of the rock. This seems to be G. Wrightii. It is somewhat 

 thickened at the ventral edge. 2. A similar but imperfect specimen, modified 

 with obhque " plaiting." Ventral border thickened. 3. Two imperfect speci- 

 mens on one slab (jre)? one of which, probably about ^o ™ch or 19 mm. long, 

 is only ^ inch or 3"5 mm. across (high). The ends are modified by cleavage- 

 pressure. This (fig. 18) approaches most nearly to Dr. Hicks's description of 

 G. Marrii. 



A specimen in the British Museum (42162, PI. XIV, fig. 17) has kept the shape 

 of its ends more perfectly, and they are more decidedly truncate than in G. 

 Wrightii, one extremity being more bluntly truncate and higher than the other. 

 Another, in the Museum Pract. Geol. (^, fig. 16), is truncate at one extremity, 

 whilst the valve, narrow throughout, tapers with a rounded end at the other ; and 

 this seems to us to be probably one of the best preserved outlines of G. Marrii. 

 It corresponds with a good specimen (hollow cast with 5^3) in the Woodwardian 

 Museum, which is 20 mm. long X 4 mm. wide, truncate at both ends, one of 

 which is wider (4 mm.) than the other (2*5 mm), and straight throughout, not 

 curved like fig. 16, and having a close relationship to fig. 17 ; whilst, with its 

 curved outline and rounded end, fig. 16 has fig. 18 for a poor representative. 



All these individuals of G. Marrii occur on the same slabs as, and generally 

 close to, G. Wrightii, It is possible that the two forms show sexual differences. 





