PARABOLINA. 61 



are the species which approach it most nearly in the characters of the head, but 

 in 0. longispinus the glabella is proportionally even shorter and considerably wider 

 than in those forms, the sides are more nearly parallel, and it is more sharply 

 truncate in front ; the eyes are placed further back and nearer to the glabella, and 

 the anterior branch of the facial suture runs inwards to the eye. In all the other 

 British species the glabella reaches nearly to the anterior margin. 



The thorax differs from that of the other British species excepting 0. mundus 

 in bearing a median tubercle upon each axial ring. 



In the shortness and breadth of the tail the species is unlike any of the true 

 Oleni. 



As has already been observed by Mr. F. R. C. Reed, 1 Olenus longispinus presents 

 several of the features characteristic of Parabolinella, and very possibly it should 

 be referred to that genus. It is in the characters of the tail and the inward course 

 of the anterior branch of the facial suture that the chief resemblance lies, but it 

 differs from the typical species of Parabolinella, in the extreme shortness of the 

 glabella, the backward position of the eyes, and perhaps in the number of thoracic 

 segments. It appears to be an intermediate form, but for the present I prefer to 

 put it in Olenus rather than in Parabolinella. 



Horizon and Locality. — Upper Lingula Flags : Dolgelly ; Moel Gron ; Penmorfa. 



Genus PARABOLINA, Salter. 



The genus Parabolina is closely allied to Olenus, but is distinguished by the 

 following characters : The glabella is long, more or less truncate in front, and 

 separated from the anterior margin by a very narrow frontal limb ; the eyes are 

 placed far forwards and very near to the anterior angles of the glabella ; the thorax 

 consists of twelve segments ; the pleurae are obliquely grooved and terminate in 

 spines ; the tail bears several spines upon each side. 



The name was originally proposed by Salter in 1849 2 for a section of the genus 

 Olenus (sensu lata), characterised by possessing twelve thoracic segments and 

 a spinose tail. Angelin elevated this section to the rank of a distinct genus. It is 

 undoubtedly a very clearly-defined group, and, as Olenus, in the wider sense, 

 includes too great a variety of forms to admit of precise definition, I propose to 

 follow Angelin's example. 



1 Geol. Mag. [4], vol. vii (1900), p. 254. 



3 Mem. Geol. Surv., Brit. Org. Rem., dec. ii, pt. ix, p. 2. 



