F. R. Coivjjer Reed— Blind Trilohites. 499 



general cephalic integument, the visual surface may very easily 

 escape detection. It is not, however, possible with our present 

 knowledge to determine positively whether the eyes were functional 

 or not. But from the analogy of other forms which were long 

 thought to be blind, and in the absence of indisputable evidence 

 that Paradoxides was devoid of the power of vision, we seem to 

 be on the safer side in holding that the long slit-like eyes were 

 of use to the animal. Moreover, it has never been satisfactorily 

 demonstrated that eyes of this type are indicative of degeneration ; 

 and if the form called ^hydrocephalus by Barrande be indeed the 

 young of Paradoxides, as supposed by Beecher,' the long eye-lobes 

 are a larval feature in the genus. The undoubted young of Olenellus, 

 which belongs to the same subfamily, show also the same feature. 

 Tlie remarks which have been made about the eyes of Paradoxides 

 would apply also to a large extent to the genera Olenellus (with its sub- 

 genera iZbtejm, Mesonacis, Olenelloides) , Plutonides, and Zacanthoides. 



The genus Anopocare of Angelin," which is described by him as 

 devoid of eyes, may be an immature Olenid, but I have not examined 

 the type. 



With respect to the genus Telephus (Barrande),^ there is some 

 uncertainty whether all the species are without eyes or whether 

 some are blind and some are not. What is taken as possibly 

 representing the palpebral lobe in some is described as the 

 cephalic border in others, and we are not in a position to determine 

 which is the correct view. Judging from the figures and descriptions 

 published, I am inclined to think that it possessed an elongated eye- 

 lobe as in Olenellus, Anopolenus, etc., and therefore that we must 

 exclude it fi-om the list of blind forms. 



We turn now to the family Illajnidee, in which it is most interesting 

 to find that the genus Illcenus contains undoubtedly a few blind 

 species. The whole head-shield of these blind forms is modified in 

 a reversionary manner, so as to exhibit characters which we have 

 seen mark a definite stage in the phylogeny of the trilohites, or 

 a particular larval stage in those forms which have a complete, non- 

 condensed, and non-accelerated development. 



In all the families above the Conocoryphidse, free cheeks bearing 

 compound eyes are the characteristic feature in the adult, and in the 

 higher and later genera the free cheeks normally exceed in size the 

 fixed cheeks and are of a triangular shape. It is only in the lower 

 forms and pre-adult stages of the higher ones that the free cheeks 

 are narrow, marginal, and band-like. But this latter primitive 

 condition of the free cheeks is found in the blind Illcsni, in which 

 the facial suture pursues a simple course subparallel to the margin 

 of the cephalon, and the fixed cheek shows no trace of a palpebral 

 lobe nor the free cheek of a compound eye. As these blind species 



1 Amer. Journ. Sci., ser. iii, vol. xlvi (1893), p. 142. 



- Pal. Scand., p. 50, pi. xx'vii, figs. 1 and 2. 



^ Barrande, Syst. SU. Boh., vol. i, p. 890, pi. xviii ; ibid., Suppl., vol. i, p. 1.5-5. 

 Angelin, Pal. Scaud., p. 91, pi. sli, fio;s. 21-3. TiJrnquist, Undersokn. Siljansom. 

 Trilobitf. : Sver. Geol. Undersokn., ser. C, No. 66 (1884), p. 89. 



