Xil PREFACE. 
very like a Cyclas.” He adds, however, that it must be an 
ocean production notwithstanding, seeing that all its contem- 
poraries in England, Scotland, and Russia, whether shells or 
fish, are unequivocally marine. 
With the exception of two of the figures in Plate X., the 
figures of the Cephalaspis and the Holoptychius, and one of 
the sections in the Frontispiece, section 2, all the prints of 
the volume are originals. To Mr. Daniel Alexander, of Ed- 
inburgh, —a gentleman, who to the skill and taste of the 
superior artist, adds no small portion of the knowledge of the 
practical geologist, —I am indebted for several of the draw- 
ings ; that of fig. 2 in Plate V., fig. 1 in Plate VL, fig. 2 in 
Plate VIII, and figs. 3 and 4 in plate X. Iam indebted to 
another friend for fig. 1,in Plate VII. Whatever defects may 
be discovered in any of the others, must be attributed to the 
untaught efforts of the writer, all unfamiliar, hitherto, with the 
pencil, and with by much too little leisure to acquaint himself 
with it now. 
