BRITISH FOSSILS. 



Decade VII. Plate IX. 



CTPHONISCUS * SOCIALIS. 



[Genus CTPHONISCUS. Salter. (Sub-kingdom Articulata. Class Crustacea. 

 Order Entomostraca. Tribe Trilobitse or Palssadse.) Body oval, convex ; head large ; 

 glabella oval, gibbous, without lobes ; facial sutures marginal in front, then in an oblique 

 and nearly straight line to the outer margin ; free cheeks very narrow. [Eyes very for- 

 ward, minute, linear.] Thorax with seven convex segments, the pleurss with fulcrum 

 and groove, their ends truncate, not produced ; tail small, of few (1 ?) segments, its axis 

 entire.] 



Diagnosis. C. minutus, glabelld Icevi, genis undique lineatis multo 

 major e; sulco verticali profundo, per genas tracto, et ad angulum posticum 

 obtusum sursum eurvato ; thoracis axi pleuras cequante ; fulcra pauilo intra 

 dimidium posito ; caud<E axi integro. 



Synonyms. Cyphoniscm socialis, Salter (1852), Report Brit. Assoc., 

 p. 57. 



This minute crustacean literally swarms in certain reddish patches 

 of the limestone at the Chair of Kildare, but has not yet been 

 observed in other localities. It is evidently a member of the Glenoid 

 group, to one genus of which, Triarthrus, it bears a strong resem- 

 blance in certain particulars. But it differs from it and all its 

 congeners in the inflated form of the glabella, which is also destitute 

 of lobes, in the small obscure eyes, and the fewness of the segments 

 of the body. The eye has not been yet discovered, and there is so 

 little indication of its place, that the animal might be supposed to 

 be a blind trilobite, but that there is no instance known of a species 

 with separable facial sutures being destitute of these organs. In the 

 very few trilobites now admitted to be without eyes, Agnostus, 

 Ampyx, some Trinuclei, &c.,^ the facial suture is soldered. The 

 converse however does not hold good, several genera with soldered 

 sutures having large and well-developed eyes. 



Description. — Length about one fourth of an inch. The general 

 form is long oval or long ovate ; the head, which is the broadest 



*' Name from Kvcpos, a convexity, and ouutkos, asellus. Linnaeus has used ' Oniscus ' for 

 small Crustacea of somewhat similar form. 



[vii. ix.] 7 I 



