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



II. acmithurus, Clarke,^ and IT. parana, Clarke,^ also from the Lower 

 Devonian. The characteristic feature of these forms, of which only 

 the pygidium and some doubtful fragments of the thorax are known, 

 is that the pleurte project over the margin of the pygidium as sliort 

 broad lappets in direct continuation and not as separate spines as in 

 Cryphceus. This character is, however, so unlike that of other groups 

 of Homalonotus that the reference of these species to this genus seems 

 extremely doubtful. !No figure of the species M. longicaudatus was 

 given in the original work referred to, but Clarke^ figures a specimen 

 from the Bosphorus under this name. 



Doubtful Members of Homalonotus. 



Of species doubtfully referred to the genus Homalonotus we may 

 mention H. ? pwictillosus, Tornquist,* from the Leptsena Limestone 

 of Sweden, which has been recorded from the Keisley Limestone * in 

 England. This trilobite, by the course of the facial sutures, seems 

 undoubtedly to belong to another genus. 



There is also one described and figured by McCoy from the Kildare 

 Limestone, Ireland, as H. ophiocephalus,^ which seems to be a hypostome 

 of some other genus, but 1 have only seen the figured example, and 

 it is somewhat poor and problematical. 



The species Asaphics hrevicaudatus (Desl.),'' which Bigot ^ has 

 removed to Corda's genus Plesiacomia,^ m^J apparently be regarded 

 as of independent generic rank, judging from the published descrip- 

 tions and figures; but I have not been able to examine any 

 specimens of it. 



Position and Affinities of Homalonotus. 



There has been considerable diversity of opinion with regard to the 

 position of Homalo7iotus sens, extenso in any general scheme of 

 clussification of the Trilobita. The genus has usually been put in 

 the family Calymenidse, and Pompecki ^° has pointed out its close 

 connexion with the genus Calymene and their probable common 

 descent from Hicks'" genus Neseuretus, and he was so much impressed 

 with the evidence of their close afiinity as to bring together under 

 one new generic name Synhomalonotus the combined groups of 

 those species of Calymene which are comprised in the C. Tristani, 

 C. Arago, and Ptychometop^is Series. But he recognized the existence 



* Clarke, " Trilob. Grez de Erere e Maecuru, Brazil " : Arch. Mus. Nac. EiO' 

 de Janeiro, vol. ix, p. 10, pi. i, figs. 9, 10, 1890. 



" Clarke, Foss. Dev. Parana, p. 97, pi. iii, figs. 5, 6. 

 ^ Clarke, " Trilob. Grez de Erere e Maecuru, Brazil," p. 14, pi. i, fig. 8. 

 ^ Tornquist, Undersokn. Siljans. Trilobitf., t. i, p. 44, figs. 46, 57 ; t. ii, 

 figs. 1, 2. 



* Eeed, Quart. Journ. Geol. Soc, vol. Iii, ]). 411, 1896. 



" McCoy, Syn. Silur. Foss. Irel, 1846, p. 53, pi. iv, fig. 4. 

 '^ Deslongcbamps, Mem. Soc. Linn. Calv., ii, pi. ii, figs. 3, 4, 1825. 

 ^ Bigot, Bull. Soc. Geol. France, xvi, p. 433, pi. v, fig. Ic, 1888. 

 '■• Corda, Prodrome, 1847, p. 55, pi. iii, fig. 30. 



'" Pompecki, Neues Jahrb. f. Miner. Geol., Bd. i, pp. 187-243, 1898. 

 ^' Hicks, Quart. Journ. Geol. Soc, vol. xxix, pp. 44, 45, 1873. 



