F. R. Coioper Reed — Blind Trilohites. 439 



must have been able to penetrate still further northward, and might 

 readily have accompanied the mammals that migrated across the 

 land-bridge formerly connecting the Palsearctio and Nearctic regions. 



In a word, if we can predicate any blood relationship between 

 the African and South American ostriches, it is certain that the latter 

 could have reached its present habitat in no other way than 

 along the route marked by Struthio camelus, S. Karatheodoris, and 

 S. Asiaticus, Struihlolithus, Diairyma, and the Ehea of Brazilian bone 

 caverns. If any will presume to deny a relationship between Struthio 

 and Bhea, they are confronted with these difficulties : to explain 

 how two separate derivatives from Carinate stock should come to 

 present such I'eraarkable similarity to one another through the 

 agency of purely fortuitous conditions, and to point out a lineage 

 for Bhea connecting it more closely with Carinates than with the 

 ancestors of Struthio. Sceptically inclined individuals are welcome 

 to regard Bhea as one of the " waifs and strays of a lost avifauna 

 left by the sea of time stranded on the shores of the present," ^ but 

 we personally prefer the more positive view, which connects the 

 New and Old World ostriches in the manner indicated. 



Further remarks on the distribution of Struthious birds, as well 

 as a more extended account of the new specimen of Struthiolithus, 

 illustrated by photographic reproductions, will be found in a 

 forthcoming number of the Bulletin of the Museum of Comparative 

 Zoology,^ of which the present paper is largely an abstract. 



III. — Blind Trilobites. 



By F. R. CowPER Eeed, M.A., F.G.S. 



Introduction. 



THE occurrence of certain genera and species of trilobites which 

 are destitute of eyes has long been known, and so much 

 importance was attached by Dalman to the presence or absence 

 of the visual organs that he instituted two principal divisions of 

 the trilobites based simply on these characters. Goldfuss followed 

 the same lines in his system of classification, though he took into 

 consideration also the structure of the eyes; and Emmrich likewise 

 regarded the possession or lack of these organs to be of taxonomic 

 value. Although in modern schemes of classification moi'e stress 

 is laid on other features of the organization, yet with our increasing 

 knowledge of the ontogeny of various species of trilobites it is 

 perceived that the presence, position, and nature of the eyes are 

 points which must by no means be overlooked. 



In a group such as the trilobites, the majority of which possess 

 ej'es, it is a matter of great interest to discover the meaning of their 

 absence in certain species and genera ; and as a result of recent 

 researches on the fauna of caves and of the deep sea the conclusion 



1 The Auk, new ser., vol. xiii (1896), p. 63. 



2 Vol. xixii. No. 7. 



