39 



whether crustaceous or chitinous, as their body-segments. That sixteen slender freely- 

 movable filamentary limbs, as restored by Mr. Woodward*, each nearly IJ inch in 

 length, attached by a flexible joint no bigger than a pin's head, and divided into 

 seven movable segments by six other joints, in a Crustacean that may have under- 

 gone, to say the least, some disturbance between death and fossilization — that the eio-lit 

 pairs of such articular appendages should remain and be found symmetrically and 

 regularly arranged across the ventral surface of the fossil, with intervals, if not parallel to, 

 yet corresponding in length with those of the thoracetral segments— presents itself to my 

 mind as much less probable than that the narrow parallel ridges which constitute 

 the observable phenomena should have had such extent of attachment to the ventral 

 surface of the several segments as to oifer the requisite physical resistance to displace- 

 ment and to loss of original regularity and symmetry of position, such as the specimen 

 of AsapJms platycephalus described and figured by Billing t actually presents to view. 

 If this Trilobite possessed the ambulatory legs ascribed to it, it could hardly be an excep- 

 tion, in this endowment, to its order, and traces of such limbs, in divers conditions of 

 displacement, would be common. 



The varied and usually more or less dislocated positions of the jointed limbs in the 

 fossil Merostomatous crustaceans would lead one to expect a like condition in other 

 families of palaeozoic fossils possessing similar appendages %. 



The difficulty of getting a clear xiQVf of the nature and affinities of Limulus at the stage 

 of anatomical investigation which had been reached before the date of the present paper, 

 and the need of such further help as could be given by one occupying himself therewith 

 by the way, as it were, and in the brief snatches of leism'e which administrative duties 

 and the cultivation of more congenial fields of original research might permit, will be 

 appreciated from the fact that one who has devoted to this qviestion so much pains, and 

 skill, and dialectic ability as the indefatigable crustaceologist Dr. Anton Dohrn has left 

 his conclusions as to the class-characters e. g. of Liimdus in a condition, to say the 

 least, not so supported as to command the common consent of his fellow labourers. 

 For myself it is a plain duty, and under responsibility for opportunities of dissection so 

 kindly and liberally aff'orded by American friends, to give my reasons for dissenting from 

 the view of Limulus being so far Arachnidan as to require, with its extinct aUies, to 

 be placed as a distinct group, not of, but by the side of, the Crustacea §. 



* Geol. Mag. viii. 1871, pi. viii. fig. t a. f Loe. cH. 



X The above considerations incline me to view, as the more probable interpretation of the appearances in this fossil 

 that given by the accomplished naturalist Dana, to whose writings, and especially those on the Crustaceous class, 

 I am indebted for much interesting and valuable knowledge. 



§ " Limulus ist zunachst verwandt mit den Gigantostraken ; beide erscheinen verwandt mit den Trilobiten, obwohl 

 diese Yerwandtschaft nicht in alle Details nachgewieseu werden kann. Die morphologisch-genealogisehen Bezie- 

 hungen dieser drei Familien zu den Criistaeeen lassen sich vor der Hand nicht feststellen, bleiben vieUeicht fiir immer 

 zweifelhaft. — Sonach bleibt uns niir iibrig, diese drei Familien unter einem gemeinsamen Namen, wofiir ich Hackel'- 

 schen Ausdruck ' Gigantostraka ' mochte in Vorschlag gebracht haben, selbstiindig zu constituireu und im Svstem 

 neben die Crustacean zu steUen." ..." Was bei Savigny andeutungsweise, bei Strauss-Diirckheim mit Einseitigkeit 

 ausgesprochen wurde, das tritt also jetzt unter dem Gesichtspunkte der Descendenztheorie von Neuem auf. Die 

 Verbindung der Arachniden mit den Crustaeeen soil durch Limulus und die ihm vcrwandten Eurypteridsn gegeben 



