ACIDASPIS. LICHAS. 15 



There is, of course, a possibility of this species, of which only the tail is known, 

 proving to be the same as A. Bobertsii, of which only the head has been found ; but, 

 as there is nothing to indicate their identity except the occurrence of single 

 specimens of each in the same locality, and as the genus is a very large one, it 

 seems safest to follow Barrande in his treatment of the kindred species A. lacerata 

 and A. radiata, and to regard them as being, as in all probability they are, separate 

 species. 



IV. Family. — LiCHADiE, Barrande. 



1. Genus. — Lichas, Dalman, 1826. 



While this genus presents many points of likeness to Acidaspis it is very easily 

 distinguished therefrom. It is notable for the complicated furrows of the glabella, 

 the frontal pair of which become longitudinal, for its large expanded tail, and for 

 the leaf-like character of its ribs and spines. It belongs chiefly to the Lower 

 Silurian or Ordovician system, only a few species occurring in the Devonian. 



1. Lichas Devonianus, Whidborne. PI. I, figs. 19, 19 a, 19 b. 



1889. Lichas Detonianus, Whidb. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Head very wide, short, and swollen, depth as great as its length, 

 ornamented with distant rounded tubercles irregular in size. Glabella oblately 

 spheroidal, very abnormal in the arrangement of the lobes ; frontal furrow becoming 

 two parallel straight lines separating a long, narrow, lougitudinally and transversely 

 convex frontal lobe, except close to the front border, where they arch rapidly out- 

 wards so that the front lobe ends in two horn-like points. The second furrow 

 running from the neck to the border at an angle of about 45°, so that the median 

 ring of the glabella becomes two large convex lobes almost equal in size to the 

 front lobe, and in shape spherical triangles. Basal ring represented by two small 

 transverse tubercles at the base of the median lobes. Cheek rather larger and 

 flatter than the median lobe, widely triangular in shape, and bearing near its front a 

 large and very elevated and oblique eye, which is surrounded by a smooth concavity 

 followed by a circle of large tubercles. Facial suture cutting the border obliquely 

 just outside the median lobe of the glabella, and proceeding on a smooth raised 

 ridge of the same obliquity up to the eye, after which it tends more outwards, and, 

 running almost horizontally, cuts the hind border close behind the cheek-spine. 

 3 



