70 MR. J. W. KIRKBY ON PERMIAN FISH AND PLANTS. 



sometimes more, are occasionally found together on a plane surface 

 of a few square feet. Such instances, however, are exceptional ; 

 and, notwithstanding that probably some hundreds of speci- 

 mens have been found since their first discovery, they cannot 

 be described as common, the quantity of specimens obtained being- 

 due rather to assiduous research than to their own abundance. 



Fully nine-tenths of the specimens found belong to a single 

 species of Palceoniscus. The remainder belong to two or probably 

 three species of the same genus, and to a species of Acroleins. 

 All the Palceonisci are small, the largest of the forms being but 

 little more than four inches in length. The Acrolepis seems to 

 have attained a length of twelve inches. 



Associated with the fish-remains, there have also rarely oc- 

 curred some fragments of plants. These, though very imperfectly 

 preserved, appear to be referable to three species, one of which is 

 a Calamites, two VlmannicB, and the fourth is a large reed-like 

 form, the generic relations of which are difficult to determine from 

 the discovered fragments. These are the only fossils that have 

 been met with along with the fish. x?o traces of Mollusca occur 

 with them, nor, as yet, of Entomostraca or other microzoa, though 

 several representatives of these classes are pretty commonly dis- 

 tributed in other parts of the Upper Limestone. 



It has already been remarked that the fossils are not altogether 

 confined to the stratum designated the fish-bed ; they are compa- 

 • ratively most abundant in that zone, and it is almost only there 

 where there is a probability of finding them by personal search, 

 their occurrence on other horizons being so rare as nearly always 

 to be the result of accidental observation rather than the reward 

 of direct investigation. Still, as they do occur at other horizons, 

 it is important that we should place on record all that is known 

 of their vertical range. 



Commencing from below, the fossils first appear in the soft 

 laminated marls at the base of the Upper Limestone, at the point 

 marked A in fig. 1 ; from this horizon two imperfectly preserved 

 examples of the common form, Palceoniscus varians, have been 

 obtained. In the slaty argillaceous limestone immediately over- 

 lying the last-named bed, and marked B in the section, a single 



