64 Proceedings of the Royal Irish Academy. 



with broad pleura concealing the short ambulatory legs. Abdomen with 

 (five or) six distinct segments, bearing at its extremity a pair of long, 

 pointed, styliform uropods. 



Type 0. ligioides, sp. nov. Upper Devonian of Kiltorcau, County 

 Kilkenny. 



A detailed description of this species may now be given. 



Length. — %Q mm. 



Head. — The small portion of the head visible from the dorsal surface 

 is about three times as broad as long. A pair of romided lobes with 

 sinuate outlines can be distinguished, and on each of these a somewhat 

 irregular area (fig. 1, o) probably indicates the position of the eye. No 

 appendage of the head can be fully made out ; but one somewhat elongate 

 antennal segment, with portion of another (fig. 1, a), can be seen on the 

 left of the anterior region of the fossil, lying alongside the front thoracic 

 segments. 



Thorax. — In the present genus, the segment (fig. 1, i) which in most 

 Isopoda is the foremost free thoracic segment appears to be fused with the 

 head, as well as the true first thoracic segment to which the maxillipeds 

 belong. The tergum of this segment is short and broad, with somewhat 

 flattened pleural margins, which at the hind corners project slightly over 

 the segment next behind. There is a central semi-elliptical lobe on this 

 tergum. From the left of the segment projects what appears clearly to 

 be part of a chelate appendage (fig. 1, c). 



The second free thoracic segment has the front lateral regions narrowly 

 rounded, and the hind corners produced into somewhat acuminate processes ; 

 a prominent ridge in form of an arc, behind which is a transverse crescentic 

 grove, crosses the front region of this tergum, and is produced backwards 

 and outwards to the hind corners (fig. 1, 2). The terga of the succeeding 

 four segments are very similar (fig. 1, 3-6). Each has the hind corners of 

 the pleura prolonged, and strong arched ridges can be traced from these 

 corners running forwards and inwards; further, a transverse ridge, nearly 

 parallel to the edge of each tergum, crosses its anterior half. On a first 

 examination of the fossil, these ridges look like the boundary-lines of terga, 

 so that the nimiber of segments appears to be two or three times as many as 

 it really is. Detailed study of the appearances shows that the segmental 

 divisions are distinct grooves with the raised hinder edge of the anterior 

 tergum in front of each ; these grooves reach the lateral edges of the animal 

 at points where the overlap of the successive pleura can be plainly seen. The 

 transverse and arched ridges, on the other hand, are not associated with any 

 clear evidence of segmentation. 



