Vol. 52.] FAUNA OF THE KEISLEY LIMESTONE. 411 



recently, but have no further particulars to add to Salter's minute 

 description of its characters. 



Only one pygidium, 4 millim. in length, has so far been dis- 

 covered at Keisley, and this must have belonged to a large 

 individual. 



Calymenid^:. 



Caltmexe Bluacexbachi, var. CARAcrAcr, Salter. 



The genus Calymene has been recorded from the Keisley Lime- 

 stone by Prof. Harkness. A glabella and pygidium belonging to 

 the above species have recently been found in the state of internal 

 casts, but exhibiting all the usual well-known characters. 



Hoatalonottjs ? prjjNrcTiLLOsrjs, Tornquist. 



Prof. Nicholson and Mr. Marr were the first to record this 

 curious trilobite from the Keisley Limestone, and in fact from 

 England. 1 But it had been collected many years previously from 

 that bed by Prof. Harkness, for I found unnamed specimens of it 

 in his collection at Carlisle. It had also been long ago found at 

 the Chair of Kildare, but was named Asaphus ? and Olenus ? It 

 is still open to doubt whether it is correctly placed in the genus 

 Homalonotus, and it appears closely allied with Billings's genera 

 Bathyurus and Bathyurelbis, to one of which it may subsequently 

 have to be referred. Tornquist describes and figures it in the 

 Swedish Geological Survey Memoirs 2 from the Leptcena- Limestone. 



Ill^enid^:. 

 Ill^enus Bowalani, Salter. 



The determination of the species or varieties of the genus lllcenus 

 has been a matter of considerable difficulty, inasmuch as the common 

 /. Bowmani varies considerably in outline and convexity of the 

 head-shield. Some specimens also show an ornamented surface, 

 whereas Salter described the surface as smooth. After carefully 

 examining a very large series of specimens I believe that I can 

 establish two fairly well-marked varieties of the typical form, and 

 these I have respectively called /. Bowmani, var. lonyicapitatus, and 

 /. Bowmani, var. brevicapitatus. The typical form of /. Bowmani 

 also occurs, and there are found some individuals which can with 

 difficulty be assigned to any of the three, for they possess inter- 

 mediate characters. 



Thus one specimen of a head-shield has all the characters and 

 the ordinary shape of the typical /. Bowmani, but its surface is 

 ornamented with raised lines as in the variety brevicapitatus. 



Again there are some head-shields of a pointed form like the 

 variety longicapitatus, but without the conspicuously sudden down- 

 ward curvature of the front end of the head-shield. 



1 Marr & Nicholson, ' The Cross Fell Inlier,' Quart. Journ. Geol. Soc. 

 vol. xlvii. (1891) p. 507. 



- B. L. Tornquist, ' Undersokn. ofv. SiljansoinrSdets Trilobitfauua,' Sver. 

 geol. Undersokn. I6ti4, p. 44, pi. i. figs. 4(5 & 47, pi. ii. figs. 1 & 2. 



