484 Dr. H. Woodward — Culm Trilohites from North Devon. 



I have detected the overlapping clearly in some of the other unfigured 

 examples of this species in the collection, due to squeezing together 

 of the thoracic rings. 



Fig. 11 is no doubt the most complete of the three, Fig. 5 having 

 been shortened by squeezing together longitudinally, which has given 

 it a greater lateral expansion. 



In all these specimens the body axis is considerably broader than 

 the pleurae, and the trilobation is very strongly marked. The pleurse 

 are strongly recurved, falcate, and their extremities rounded and 

 broadly faceted. 



The pygidium is very short, the axis is truncated and does not 

 reach the posterior border, the coalesced segments are obscure, but 

 appear to be about six or seven in number, the margin when 

 preserved has a well-marked rim (see Fig. 11). 



Although in the genus Proetus there are several species having 

 a larger number of coalesced segments in the pygidium than are 

 seen in this form from Coddon, yet there are many others with an 

 equally short pygidium. On the other hand, there is no Phillipsia 

 nor Grifithides with such a shortened tail-shield, nor can the 

 head-shield, although certainly less well preserved, be referred to 

 either of these genera. 



Several forms, at present within the genus Proetus, will un- 

 doubtedly have to be removed whenever this genus is revised. 



Proetus, sp. (PI. XX, Fig. 12.) 



This large pygidium, in which the traces of coalesced segments 

 are almost obliterated, is figured on our plate of the natural size. 

 It measures 29 mm. in width, by 15 mm. in length ; the surface 

 is very convex, the axis is 11 mm. broad at its union with the 

 free thoracic segments, and diminishes to 4 mm. near its rounded 

 distal extremity, which almost touches the posterior border. Traces 

 of about two or three coalesced segments can be discerned near the 

 proximal bolder. The outer margin had a raised thickened rim. 

 The late Professor James Hall, in his " Palseontology of New 

 York," has figured a somewhat similar smooth pygidium, which he 

 named Proetus crassimarginalus, from the Upper Helderberg Group 

 (Devonian),^ but it is longer in proportion to its breadth than is our 

 Coddon Hill specimen. There are no free segments or head-shields 

 known from this horizon which can be relegated to this pygidium ; 

 I do not therefore propose to give it a name. It may, for the present- 

 be referred to the genus Proetus. 



As a large number of these Culm-measure Trilobites are more or 

 less in the condition of compressed and distorted casts, it is often 

 very difficult to determine accurately their minute characters ; it is 

 better, therefore, to defer a fuller description of them until, as is 

 to be hoped, more perfect materials are obtained. 



Griffithides Barkei, sp. nov. (PI. XX, Fig. 14.) 



This is a characteristic example of the genus Griffithides, and may 



1 Pal. New York, 1888, vol. yii, pi. xx, fig. 8. 



