1857.] KIRKBY PERMIAN FOSSILS. 215 



the integument the cephalic region is small, being less than the 

 next succeeding segment ; but this fact, which is very constant in 

 the adult animals, is not permanent in the larval condition of the 

 same ; the head or cephalic segment being more important in rela- 

 tion to the succeeding rings. But from all the larval or adult forms 

 of prominent-eyed Isopods this fossil specimen differs in the anterior 

 position of the eye. This may be a specific distinction only. 



'* The fact that this Isopod, found in so early a geological period, 

 assumes rather the larval than the adult form of the recent type, is 

 consonant with all we know of the relation which animals generally 

 of so early a date hold to existing species." 



AVe must therefore, it appears, look upon our fossil Crustacean 

 as belonging to the family Isopoda, though somewhat of an ab- 

 normal character in reference to the recent forms. 



Baron Schauroth's specimen from the Zechsteiu-dolomite of Poss- 

 neck appears to consist of four body-rings and the two posterior 

 segments ^. I have been fortunate, however, in procuring one speci- 

 men showing the cephalic segment or carapace, with two body-seg- 

 ments attached (PL VII. figs. 1, 2, 3). 



The carapace is about as long as four of the succeeding body- 

 rings, somewhat less in depth, and slightly compressed laterally ; it 

 is carinated along the back and wedge-shaped in front ; the eyes are 

 large, round, and prominent, and are placed far forward ; from the 

 lower part of each eye runs an indented line, at a short distance from 

 the margin, up to the dorsal region, where it curves forward. 



The other five specimens consist of body-rings (2 to 6 in number) 

 and the two great posterior or caudal segments t ; and are very 

 similar to the figures given by Schauroth. In one of the Durham 

 specimens (fig. 7) there are six body-rings, and two posterior seg- 

 ments ; the others (figs. 4, 5, 6) have likewise the two latter seg- 

 ments, but not so manv of the former. The bodv-se^ments are 

 narrow, almost uniform in size, but varying a little in depth, the 

 central ones appearing to be the most produced ; they overlap each 

 other and the penultimate segment posteriorly ; they are slightly 

 compressed, and have traces of a median dorsal ridge ; those in frpnt 

 have their extremities turned a little forward, while the posterior 

 ones are bent in the contrary direction. The large penultimate seg- 

 ment is greatly developed laterally ; it is strongly carinated dorsally ; 

 its ventral margins are slightly convex, as is also the posterior border, 

 which has a deep notch not far from the dorsal ridge ; the ridge or 

 keel of this segment is very prominent except anteriorly, where at 

 each side of the dorsal line is a transverse swelling ; it is com- 

 pressed also posteriorly. The next segment, which is the hinder- 

 most known, is more compressed than the preceding one, and con- 

 siderably smaller. 



None of the English specimens show the true external surface, 

 nor have any traces of feet or of antennae been found. 



* The latter are regarded as the cephalic and thoracic segments by this author. 

 t It is probable that we have all the hinder segments in these specimens ; but 

 there may possibly be a small terminal one besides. 



