Dr. F. R. Gowper Reed — The genus Homalonotus. 271 



and that the " trilobation is conspicuous but not deep" (p. 105). 

 The latter statement is made for the type species and is incorrect, 

 the axial furrows being very shallow and the pleural portions of the 

 thorax scarcely marked off from the axis in the general convexity of 

 the body. In the pygidium, however, the axis is well defined, has an 

 independent convexitj' and well-marked though not deeply impressed 

 axial furrows. In the thorax the axial furrows form continuous 

 depressions, but each axial ring is independently marked off from its 

 pleura by a short oblique transverse furrow corresponding to the one 

 crossing the neck ring from the base of the glabella, which Salter 

 mentions and shows in his figure (woodcut 24 on p. 106). The base 

 of each pleura is somewhat swollen in the angle between this 

 transverse furrow and the pleural furrow which is a lateral continua- 

 tion of the furrow separating off the articulating band on the axial 

 ring. There is a peg-like interior projection situated on the posterior 

 margin of the thoracic ring just inside the posterior end of the short 

 transverse furrow, and this peg or knob fits into a small corresponding 

 notch on the anterior margin of the succeeding ring. Salter shows 

 this structure (op. cit., pi. x, fig. 16) in his figure of a segment of 

 IT. Brongniarti, Desl., but does not describe it in connexion with 

 H. bisulcatus. 



In the case of the pj-gidium the shape is semi-oval or parabolic in 

 all the typical Shropshire specimens; the so-called "young one"^ 

 from North Wales, figured by Salter (op. cit., pi. x, fig. 8), is certainly 

 different. Salter's description of the typical form, however, is correct, 

 and it is important to notice that the axis is composed of 1 1-12 rings 

 and is continued to the margin by a " conical appendage" or post- 

 axial angulated triangular piece. There is also a distinct (though 

 very narrow) flattened or gently concave border, not sharply defined 

 from the rest of the pleural lobes, but the pleurae do not cross it. 

 The first sulcus crossing the lateral lobes is a direct continuation of 

 the one on the axis which separates off the articulating band at its 

 front end; we may therefore suspect that the second similar strong 

 one is of the same nature, and therefore not a true interpleural furrow 

 but homologous with the pleural furrows of the thorax. This opens 

 up a curious question as to the nature of the so-called pleurae on the 

 pygidium. It was from the presence of these two strong furrows 

 that Salter termed the species bisulcatus. 



The original Welsh specimens from the Bala beds south-west of 

 Pwllheli which Salter referred to H. itsulcaius and figured as such in 

 1852^ are undoubtedly distinct from the Shropshire types; the 

 middle-shield (fig. 25), by its breadth, shortness, and flattened anterior 

 edge, suggests a reference to If. Sedgivichi, and perhaps the pygidium 

 (fig. 28) may belong to the same species. Eut both specimens are 

 poor, cruslied, and distorted. 



The other Welsh specimen figured as B. bisulcatus in his mono- 

 graph in 1865 (pi. X, fig. 6) is likewise much distorted; it is from 

 ^loel y Garnedd, Bala, and together with some similar fragments in 

 the Jermyn Street Museum (-s\-, -^^2, -5-r) from the same locality may 

 belong to a new species. 



^ Salter, op. cit., pi. i G, figs. 25, 28. 



