248 BRITISH FOSSIL CRUSTACEA. 



This new species, of which there are two examples, both figured in our PI. XXXI, 

 figs. 7 a, b, exhibits the most complete anchylosis and obliteration of the divisions of its 

 body-segments of any of the Coal Limuli. The entire body measures 8 lines in length, 

 and 8 in greatest breadth ; of this the head-shield measures 4 lines in length, and 8 in 

 breadth ; the anterior (thoracic) part of the post-cephalic shield is 6 lines broad, 

 diminishing to 2 lines near the posterior (abdominal) part ; length of the thoracico- 

 abdominal somites 4 lines. The telson measured 4 lines in length. The head-shield is 

 very tumid, the posterior genal angles are not produced ; the glabella is divided down 

 the centre by a slender ridge ; its front border (as in most other species) forms two 

 arches, between which and in front of the head-shield, the larval eye-spots are seen ; 

 the small compound eyes are placed midway upon the lateral border of the glabella. 



The divisions of the thoracico-abdominal segments are only faintly indicated along 

 the central axis of the body ; the margin does not show the usual serrations or spines, 

 as in the other species ; but the number of segments appears to have been the same. 

 The coalesced abdominal segments were marked by a very prominent spine or tubercle, 

 the top of which has, however, been broken off. 



I have named this species Prestwichia Birtwelli, after its discoverer, Mr. Thomas 

 Birtwell, in whose collection the specimens are preserved. 



Genus 4. — Cyclus, Be Koninck. 1841. 



Cyclus, De Koninck, 1841. Descript. Animaux Foss., p. 591. 



— Salter and H, Woodw., 18G5. Cat. and Chart Foss. Crust., p. 17. 



— H. Woodw., 1868. Brit. Assoc. Rep. Norwich, p. 72. 



— 77. Woodw., 1870. Geol. Mag., vol. vii, p. 554. 

 Agnostus, Phillips, 1S36. Geol. Yorkshire, vol. ii, p. 240. 



In my fourth Report to the British Association (1868) I described, among other 

 Crustacea, two species belonging to the genus Cyclus, one of which still remains unique. 

 Since that date I have, by the kindness of Professor T. Rupert Jones, F.R.S., received a 

 number of specimens of this genus, collected by Professor Harkness, F.R.S., Mr. Joseph 

 Wright, F.G.S., of Belfast, and Mr. J. H. Burrow, of Settle, Yorkshire; from the Carbo- 

 niferous Limestone, which I described in the ' Geological Magazine ' for 1870, p. 554. 



Prof, de Koninck, of Liege, the founder of the genus Cyclus, has made the following 

 remarks thereon : 



" There is no doubt this animal should be ranged with the Crustacea, and in Milne- 

 Edwards's order Trilobita abnormalia and Battoidea, near to Agnostus." 



M. de Koninck also considered it probable that the body of Cyclus was soft and 

 very contractile, that it was a parasite, and that the two tubercles which we have called 



