424 



MR. H. M. BERNARD ON THE 



[Aug. 1894, 



Fig. 



10. — Pygidium of 

 Calymene Blumen- 

 bachii. 



head of Olenellus there can, I think, be no doubt, and as little, all 

 things considered, that this oval patch on the head of Olenellus asa- 

 phoides is homologous with the oval patch on the head of Apus. If so, 

 it was, in all probability, originally excretory, and its transformation 

 into a spine suggests that this spine was poisonous. It is, further, 

 interesting to note that this median head-tubercle or spine tends to 

 be repeated on the trunk-segments. 



VI. The alimentary canal of the trilobites, as is well known, has 

 been found more than once as a cast within the animal, due, 

 according to Barrande, 1 to its having been filled with argillaceous 

 matter, which suffered no change if the matrix of the fossil happened 

 to be sand. In this connexion, I 

 might mention that I have a series 

 of sections of Apus cancriformis in 

 which the alimentary canal is full, 

 almost to distension, of fine grit. 



Burmeister, arguing from analogy, 

 placed the anus of the trilobites 

 terminally, as indeed he was quite 

 justified in doing, considering that 

 he correctly interpreted the pygidium 

 as composed of fused segments. 1 do 

 not quite understand the figure given 

 by Burmeister (op. cit. pi. v. fig. 4), 

 which seems to represent an anal 

 aperture in Asaphus tyrannus. If 

 this be so, the anal segment in this 

 animal seems to be greatly specialized, 

 and the position of the aperture 

 figured (on the ventral surface of the 

 segment) may have been secondarily 

 acquired. I have myself discovered, 

 by means of the sand-blast, clear 

 traces of an anus in Calymene Blu- 

 menbachii (see fig. 10, a & b), and it is 

 situated terminally, as one would 

 expect. This position of the anus 



could further be gathered from what is known of the course of the 

 alimentary canal. Barrande (p. 229) describes it as running 

 backwards " jusqu'a l'extremite de l'axe, vers le bord posterieur du 

 pygidium." 



VII. With regard to the limbs of the trilobites, the most important 

 recent discovery 2 has been that of antennae in Triarthrus Bedcii 



1 ' Systeme silurien de la Boheme,' vol. i. (1852) p. 229. 



2 W. D. Matthew, 'On Antennae and other Appendages of Triarthrus 

 Beclcii' Amer. Journ. Sci. ser. 3, vol. xlvi. (1893) p. 121. By the kindness of 

 Dr. Henry Woodward I have been able to examine a specimen with antennae, 

 presented to him by Prof. Marsh and exhibited by him in the Natural 

 History Museum at South Kensington. I have no word to add to Mr. Matthew's 

 careful description. 



a blinder surface, showing 

 the torn edge of the ven- 

 tral membrane running 

 posteriorly towards the 

 median anus. 



6=The same, as first revealed 

 by the sand-blast. The 

 projecting portion of the 

 membrane bounding the 

 anus anteriorly was acci- 

 dentally broken off. 



