ILLSENUS LATHS. 63 



7. Illsenus latus, M'Coy, 1840. Plate IX, figs. 6, 7. 



1849. Illsenus latus, M'Coy, Ann. Mag. Nat. Hist, [2], vol. iv, p. 404. 



1854. Illsenus latus, M'Coy, Synops. Brit. Pal. Foss. Woodw. Mm., p. 172, pi. 1 e, figs. 17, 



17a. 



■ — Illsenus latus, M'Coy, Contrib. Brit, Palaeont,, p. 143. 



1867. Illsenus bowmanni !, Salter, Mon. Brit, Trilob., p. 215, fig. 55. 



— Illsenus crassicauda ?, Salter, ibid., p. 215, fig. 56. 



1873. Illsenus crassicauda?, Salter, Cat. Camb. Sil. Foss. Woodw. Mus., p. 34. 



1876. Illienus crassicauda ?, Armstrong and Young, Cat, West Scot. Foss., p. 16. 



1879. Illsenus bowmani, Nicholson and Etheridge (e.p.), Mon. Sil. Foss. Cirvan, fasc. ii, p. 155. 



— Illsenus crassicauda, Nicholson and Etheridge, ibid. p. 160. 



Remarks. — There are several specimens of pygidia from Minuntion in Mrs. 

 Gray's collection which resemble the one figured by Salter (op. cit.) as Illsenus 

 crassicauda, Wahl. (?) from the Llandeilo Limestone of Knockdolian, and also 

 agree with those from the same locality in the Woodwardian Museum similarly 

 named by Salter. One of the latter Avas mentioned by M'Coy (op. cit.) as probably 

 belonging to a young individual of his species I. latus, which was founded on an 

 imperfect head-shield from Wrae Quarry, Tweed. Salter, however, was of the 

 opinion that this specimen should be attributed to I. bowmani, and that accordingly 

 M'Coy's species I. latus could not stand and that the name must be dropped. 

 The specimens from Bugon, Knockdolian, in the Woodwardian Museum, which 

 Nicholson and Etheridge refer to (op. cit., p. 160) as the sole evidence of the 

 occurrence of I. crassicauda in the Girvan area, are these very specimens 

 which Salter and M'Coy mentioned, and they include the above mentioned 

 small pygidium of /. latus ?, a few thoracic segments and a much crushed 

 head-shield. 



In Mrs. Gray's collection from Minuntion there is one imperfect and 

 poorly preserved head-shield which closely resembles M'Coy's /. latus, and it is 

 associated with pygidia from the same locality, like Salter's /. crassicauda. This 

 head-shield is about twice as wide as long, is flattened posteriorly, but strongly 

 bent down and convex anteriorly, with a short broad glabella about half the 

 width of the head-shield and with very broad fixed cheeks; there is a distinct 

 occipital furrow as in I. bowmani, and the eyes appear to occupy a similar 

 position. 



The pygidia vary from one and a half times to twice as broad as long, and arc 

 flattened or feebly convex, bent down at the sides and posteriorly; the lateral 

 angles are truncated almost at right angles to the front margin, and the sides of 

 the pygidium are thus straight and abrupt. The fulcrum is situated at about two 



