496 F. R. Cowper Reed — Blind Trilohites. 



is considered by some palasontologists to be identical with S'arpides 

 (Beyrich) ; but Harpides is described and figured as possessing eye- 

 spots, whereas Erinnys has merely the branching nervures on the 

 cheek, and there are other important differences in its structure 

 which apjDcar amply sufficient to separate it generically. 



Carausia (Hicks) ^ is in every respect closely allied to Erinnys, 

 and neither genus shows any free cheeks or dorsal facial sutures. 

 Both genera are found in the Menevian beds. 



Dictyocephalites (Bergeron) may eventually pi'ove not to be a blind 

 form. It occurs in the Ordovician of Saint-Chinian, but only two 

 imperfectly preserved specimens of it are known. Bergeron con- 

 siders that it shows resemblances to Eiirycare (Angelin), but the 

 structure of the head is more suggestive of Harpides, and the 

 tubercles on the cheeks resemble eye-spots. 



In America there are the genera Avalonia (Walcott) and Bathy- 

 notus (Hall), which, however, may possibly not be blind. Haritia 

 (Walcott) is probably only of subgeneric rank. 



Beecher (loc. cit.) says in his concluding remarks on this family 

 that " the general average of the characters in the ConocoryphidEe 

 represents the main larval featui'es throughout the other families " 

 of the order Opisthoparia to which it belongs. 



The genus Carmon (Barrande) - is placed by Beecher in this 

 family, but ZitteP puts it with the Proetidee. Only two species of 

 this genus have been described. Of these the first, C. mutilus 

 (Barr.), occurs in Etage J)d 5, and the second, C. primus, in J)d 1. 

 The important point for us to notice is that C. mutilus has no eyes 

 or facial suture, whereas C. primus possesses both. Barrande (loc. 

 cit.) says these differences are only of specific importance, and he 

 instances Illcenus, with its blind and eye-bearing species, as an 

 analogous example. Such may be the true explanation, and it 

 is especially probable to be so if the true affinities of Carmon 

 are with the Proetidse. But C. primus is only known to us by 

 a head-shield, and though according to Barrande the hypostome 

 of C. mutilus resembles that of Proetus, yet the thoracic segments 

 and pygidium are more suggestive of the Conocoryphidse. If its 

 real relations are with the latter family we must regard C. mutilus 

 as a solitary survival of a primitive type, and C. primus then probably 

 belongs to a different and higher genus. If, on the other hand, 

 we consider that its general characters indicate affinities with higher 

 and eyed forms, such as Proetus, we must either regard the absence 

 of eyes and the primitive characters of the head-shield as a sign 

 of reversion or degeneration, probably conditioned by a certain 

 environment, or as an analogous case to Areia, which I have 

 described * as a primitive form belonging to the Cheiruridfe, in which 

 the normal ontogenetic development has been arrested, irregularly 



^ Quart. Journ. Geol. Soc, vol. xx-^dii (1872), p. 178, pi. vi. 



2 Barrande, Syst. Sil. Boh., vol. i, p. 915, pi. xsxiv, fig. 43. Ibid., Suppl., 

 vol. i, p. 19, pi. ii, figs. 4-6 ; pi. xiv, fig. 43. 



3 Handb. Palseont., vol. ii, p. 625. 



* Geol. Mag., Dec. lY, Vol. V (1898), p. 206. 



