BRITISH FOSSILS. 



11 



Section Cheieubus proper. 

 Glabella with the furrows all distinct, but not meeting across. 



2. Ch. speciosus. Dalm. sp. — above described. 



3. Ch. gelasinosus, Portlock. Amphion gelas. id. Geol. Eep., t. 3. fig. 4. (head) ; and 

 Arges planospinosus, pi. 5. fig. 9. (tail). Cheirurus, Beykich (1845), Bohm. Tril., 1. p. 19. 

 Salter (1851), Quart. Geol. Journ., vol. vii. pi. 8. fig. 1. Cheirurus planispinosus, Bronn. 

 Ind. Pal. (1848). 



Ch. depressus, capite transversa, glabella rectangulari sulcis brevibus transversis, lobo 

 frontali brevi, basalibus oblongis transversis vix circumscripiis, uno ab altera spatio cequali 

 sejuncto ; genis latis, marginibus depressis, spinis brevibus ; canda (Jiic hand dubie referta) 

 lata, segmentis utrinque tribus latis, ad basin longe adnatis, acuminatis ; primo in appendicem 

 longam producto secundum longe excedente, hoc tertium brevem superante ; axi A-annulato, 

 articulo ultimo minimo angusto, nec apicem caudce profunde emarginatum attingente. 



The upper lobe of the glabella is not at all broader — sometimes it is narrower — 

 than the rest ; and in the furrow beside it there is a very deep indentation. On the 

 under side of the crust this would be a strong ridge, to which, as Barrande has 

 shown, the processes of the hypostome are attached. The transverse form of the 

 head, especially the wide cheeks, easily distinguish this from any other species. 

 The surface of the glabella is smooth, or nearly so. 

 There can be little doubt that, as Beyrich has suggested, the head and tail belong to 

 one animal. They are alike broad and depressed, and agree in size, while no other 

 species of the genus occurs with them. 

 Locality. — Co. Tyrone, head and tail ; limestone of Ayrshire, head only. [Presented 

 by Mr. C. Moore.] 



4. Ch. cancrurus. sp. n. — Ch. satis magnus, caudd lineas 20 lata transversa, apice abrupte 

 truncato prcemorso ; axi lato, annulis quatuor subcsqualibus, tertio d quarto punctis binis 

 remotis solum separata; lateribus spinis quatuor langis sub-par allelis, ad basin adnatis^ 

 transversiSf apicibus lente decurvatis; basalibus utriusque lateris longa intervallo remotis. 



A most remarkable species, in which the four lateral lobes of the tail start hori- 

 zontally from the broad axis, instead of gradually converging beneath it, and 

 leave its apex bare ; the breadth of this space being increased by the outward 

 direction of the spines themselves, which begin to curve downwards only when 

 when they have attained half their length. The appearance of the perfect tail is 

 just like that of a crab ; prcemorsus might have been an appropriate specific name. 

 C. obtusatus, a Bohemian species, somewhat resembles this, but the spines are 

 radiating, not parallel. 



There is a rare cephalic shield in the Chair of KUdare limestone, which may very 

 probably belong to this species ; it is as unusual in its character as the tail we have 

 described. It is the Ch. gelasinosus of M'Coy's Synopsis Sil. Foss. Ireland, 44. 

 The cheeks are scrobiculate, and the eyes forward, the glabella smooth, clavate, long, 

 and narrow ; the neck furrow trends upwards towards the middle on each side ; the 

 basal furrows curve downward, but do not meet the neck furrow, or quite circum- 

 scribe the subtriangular basal lobes ; the middle furrows are strong and transverse, 

 the upper pair apparently obsolete (probably some faint traces of them may be 

 found.) But there is enough to distinguish the species as a very curious one, and 

 provisionally I refer it to the C. cancrurus, with which it agrees well in size. 



Locality. — Limestone of the Chair of Kildare in Ireland, [tail in Survey coll. ; sup- 

 posed head in the cabinet of Mr. K. Griffith.] 



5. C. octolobatus. M'Coy's Synopsis Pal. Foss. Woodw. Mus., t. 1 G. f. 10. [Mem. 

 Geol. Surv., vol. ii. pt. 1. pi. 7. fig. 36, without name.] 



C. pygidio transversa elliptico semiunciali, bis quam longa latiori, margine octolobato ; axi 

 deprcsso, annulis ti'ibus, duohus superior ibus suhceqnalibus, tertio lata a limbo terminali punciis 



