158 Professor C. E. Beechcr — Stnichire of TriloUtes. 



in sections, in fig. 3, pi. iii of Walcott's paper, and of Ceraurus, in 

 fig. 2 of the same plate. During a recent visit to the Museum 

 of Comparative Zoology, the writer examined many of the sections 

 made by Walcott during his long and successful search for trilobite 

 appendages. The structure shown in the figure here given (Fig. 4) 



Pig. 4. — Transverse section througlithe thoracic region of Cahjmene senaria, Conrad; 

 after "Walcott ; to show the folds of the ventral integument and the basal joints 

 of the legs, with their points of attachment at the sides of the sternal arch. 

 Enlarged three diameters. 



was verified, and other sections were observed in which the folds 

 were more pronounced, sometimes extending as thin laminee into 

 the body-cavity, thus having the character of a normal apodeme. 



Fig. b. — Asaphus megistos, Locke. A reduced outline of the figure published by 

 iVIickleborough ; showing the endopodites in the pleural areas, with the gnatho- 

 bases extending obliquely inward from the sides of the axis, and in the posterior 

 thoracic median line the ridges or folds of the ventral integument. One-half 

 natural size. 



The second instance to be noted, where the ventral membrane 

 has previously been illustrated, is a specimen of Asaphus megistos, 

 Locke, first described by Mickleborough ' from the Cincinnati shales 

 in Ohio. In his figure, an outline of which is here reproduced 

 (Fig. 5), there are shown a number of discontinuous longitudinal 

 lines in the axis of the posterior thoracic region. Mr. Charles 



1 Op. cit. 



