428 



MR. H. M. BERNARD ON THE 



[Aug. 1894, 



that the limbs in Calymene, as in Apus, had long transverse lines of 

 attachment. Further, the shape of the limbs of Apus in section 

 is almost exactly the same as the sections of the limbs shown in 

 Calymene senaria. This comparison with the section of Apus makes 

 it very clear that the section (fig. 13) passed through the mem- 

 branous basal portions of the limbs of Calymene, and does not contain 

 longitudinal sections of the legs themselves, showing traces of joints, 

 as Walcott very naturally, but I thiuk erroneously, infers. 



Fig. 15. — A more tangential 

 longitudinal section of 

 Calymene senaria. (After 

 Walcott.) 



Fig. 16. — Corresponding section of 

 Apus (Lepidurus) spitzbergensis, 

 Bernard. 



That the limbs in the trilobites had long transverse insertions, as in 

 Apus, seems to me also to be established by fig. 1 7 (from Walcott), 

 which represents a rolled-up Calymene senaria with a portion of the 

 dorsal test broken out, showing a cast of the ventral surface. From 

 this we see that the limbs were certainly, at their origin at least, mem- 

 branous lobes which sloped forward, as shown in fig. 13 (p. 427). Wal- 

 cott himself does not seem to have allowed for this forward slope, in 

 concluding from his sections that 



Fig. 17. — Enrolled Calymene. 

 (After Walcott.) 



the membranous lobe had but 

 comparatively a short transverse 

 attachment, the limb afterwards 

 swelling out transversely into a 

 flat triangular basal piece. If 

 the plane of transverse section 

 passed through the apex of one 

 of the bent 1 black lines repre- 

 senting the lines of insertion 

 of the limbs in fig. 17, we 

 should get exactly the appearance 

 adopted by Walcott in his ideal 

 restored section, i. e. a broad 

 basal joint with narrow attach- 

 ment. Further, Walcott's own sections show in other places that 

 the line of insertion was in reality not so short. 



Judging, then, from these valuable sections compared with trans- 



1 I cannot be quite sure whether I am interpreting the figure correctly ; part 

 of the lighter lines may be meant to represent dorsal muscular apophyses. This, 

 however, would not affect the main argument. 



[The dorsal test is broken, showing a 

 cast of the inner ventral surface.] 



