THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XIV. — The Ventral Integument of Trilobites ; by C. E. 

 Beecher. (With Plates II-Y.) 



In previous papers by the writer, on the structure and 

 appendages of Triarthr us^* no attempt has been made to 

 describe or illustrate the character of the ventral integument, 

 especially in the sternal or axial region. The specimens 

 hitherto described were prepared to show details of the append- 

 ages, and though portions of the ventral membrane were 

 exposed in many individuals, the subject was not considered of 

 sufficient moment to warrant a distinct study, particularly' as 

 no characters were observed in the cuticle that had not been 

 previously seen in more or less perfection by Walcott 10 in the 

 genera Ceraurus and Calymmene. A recent discovery by 

 Jaekel, 8 however, necessitates the separate consideration of 

 this structure. This necessity arises from the fact that a posi- 

 tive addition to the knowledge of the trilobite anatomy may 

 be deduced, although, as will be shown, Jaekel was apparently 

 entirely misled in his interpretation of the nature of his dis- 

 covery. 



In the paper under discussion, Jaekel 8 states that the occa- 

 sion for his publication arose from the finding of a specimen 

 of Ptychoparia striata, from the Cambrian of Bohemia, in 

 which some structures were preserved in the axis of the six 

 anterior segments of the thorax. These, he asserts, are the 

 proximal joints of the legs. 



The specimen was preserved as a cast in a rather coarse- 

 grained sandstone, and is exposed from the dorsal side. From 

 certain surface indications of lines in the cast, Jaekel was led 

 to follow these into the rock filling the axis, and succeeded in 



Am. Jour. Scl— Fourth Series, Vol. XIII, No. 75. — March, 1902. 

 12 



