CARBONIFEROUS FOSSILS OF lERLAND. 163 



This species is distinguished from the P. truncatula, by having but ibur instead of six rows of tubercles 

 on each lobe ; it is also very much smaller and rather more pointed posteriorly. The same character distin- 

 guishes it from the P.gemvmlifera, P. Kellii, P. longispina, &c. Length of pygidium four lines, width five 

 lines. 



Phillipsia truncatula. Phil. sp. 



Asaphus truncatulus. Phil. Geol. York. — Phillipsia ornata. Portk. Gcol. Rep. 



Sp. Cli. — Pygidium large, obtusely pointed, lateral lobes flattened ; mesial lobe narrower, tumid ; cacli lobe 



with six longitudinal rows of rounded tubercles. 



I have not seen either the head or abdomen of this species. Length of pygidium nine lines, width eleven 

 lines. 



DiTHYEocARis. Scouler. 



As my friend Dr. Scouler has not as yet fully published his views concerning this very important and cu- 

 rious genus, I shall not offer any observations upon it. 



DlTHYROCAEIS COLEI. Portk. 

 Dithyrocaris Colei. Portk. Geol. Rep. 



Sp. Ch. — Longitudinally oval ; anterior end narrow, having a shallow, rounded sinus in front, posterior 

 end broader ; margins sigmoidally curved, forming an acute sinus towards the centre ; sides terminating in acute, 

 angular, flattened spines ; the mesial ridge strongly crenated ; lateral ridges almost as large as the mesial one, and 

 similarly crenated ; short, sigmoidal, anterior ones also similar ; margins of tlie valves obliquely striated ; surface 

 otherwise perfectly smooth. 



This large species is very closely allied to the Argas tricornis, Scouler. Taking one half of the shield, or 

 one valve, its length is about twice and a half the width. Length of single valves three inches seven lines, 

 width one inch six lines. 



Dithyrocaris orbicularis. Portk. 



Dithyrocaris orbicularis. Portk. Geol. Rep. 



I have only seen a few fragments, probably of this species ; along with the last, it is distinguished by its 

 nearly circular outline, and its tuberculated lateral and mesial ridges and margin. 



Dithyrocaris ScouLERL MCoy. (PI. XXIIL fig. 2). 



Sp. Ch. — Length of expanded pair of valves very slightly exceeding the width, surface smooth ; central 

 and lateral ridges transversely wrinkled ; frontal notch nearly as deep as wide, rounded. Valves, when spread 

 flat, forming a nearly orbicular shield, the length very slightly exceeding the width, and having a deep, rounded 

 notch in front ; central ridge or hinge strong, rounded, regularly marked with transverse wrinkles ; lateral 

 ridges marked with irregular, flat, scale-like undulations ; intermediate short ridges nearly straight, slightly 

 bent towards the central ridge above, and towards the lateral ridges below ; surface smooth ; margin of the valves 

 narrow, fringed or obliquely striated, immediately within which, on the lateral margins, is a plain, rounded 

 ridge, divided longitudinally by a nearly mesial sulcus ; it is close to, and parallel with the outer margin for 

 about the upper half of its length, then gradually turning in towards the lateral ridge, where it widens ; tail ex- 

 actly equalling the body in length, terminating as usual in three spines of nearly equal length, the central one 

 triangular, marked with very fine, oblique striae, meeting at an acute angle on the central ridge ; two lateral 

 spines rounded, coarsely sulcated longitudinally. Width of the expanded pair of valves one inch four lines, 

 length to the tip of posterior spine one inch five lines, length of central spine of tail one inch. 



