350 THE CANADIAN NATURALIST. [Yol. vi. 



not to be looked for in free-moving legs. The curve in these 

 arches, although it implies a forward ventral extension on either 

 side of the leg-bearing segments of the body, does not appear to 

 afford any good reason for doubting the above conclusion. It is 

 probable that the two prominences on each arch nearest the 

 median line of the body, which are rather marked, were points of 

 muscular attachment for the foliaceous appendage it supported. 



With the exception of these arches, the under surface of the 

 venter must have been delicately membranous, like that of the 

 abdomen of a lobster or other macrouran. Unless the under sur- 

 face were in the main fleshy, trilobites could not have rolled into 

 a ball. 



Supposed Legs of Trilobites.— Mr. Henry "Woodward, of 

 the British Museum, in a reply to the paper by the writer in 

 volume i, p. 320, of the present series of this Journal, supports 

 the view that the supposed legs are real legs. He says that the 

 remark that the calcified arches were plainly a calcified portion of 

 the membrane or skin of the under surface is " an error, arising 

 from the supposition that the matrix represented a part of the 

 organism." But Prof. Yerrill, Mr. Smith and myself are confi- 

 dent that there is on the specimen an impression of the skin of 

 the under surface, and that this surface extended and connected 

 with the arches, so that all belonged distinctly together. 



Moreover the arches are exceedingly slender, far too much so 

 for the free legs of so large an animal ; the diameter of the joints 

 is hardly more than a sixteenth of an inch outside measure ; and 

 hence there is no room inside for the required muscles. In fact, 

 legs with such proportions do not belong to the class of Crust- 

 aceans. Moreover the shell (if it is the shell of a leg instead of a 

 calcified arch) is relatively thick, and this makes the matter worse. 



We still hold that the regular spacing of these arches along the 

 under surface renders it very improbable that they were legs. 

 Had they been closely crowded together, this argument would be 

 of less weight ; but while so very slender, they are a fourth of an 

 inch apart. Mr, Wooward's comparison between the usual form 

 of the arches in a Macrouran and that in the trilobite does not 

 appear to us to prove anything. We therefore still believe that 

 the specimen does not give us any knowledge of the actual legs of 

 the trilobite. Mr. Woodward's paper is contained in vol. vii No. 

 7, of the G-eological Magazine. j. D. d. 



