80 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



While there is no way in which the location of these sections in the thorax can be posi- 

 tively determined, it is probable that they came from the anterior end. In sections further 

 back, supposed to be in the posterior region of the mesenteron, no sheath is shown, but the 

 canal is nearly if not quite as large in relation to the size of the axial lobe. 



The single section through the glabella (specimen 97) is of course important and for- 

 tunately well preserved (fig. 22). It shows the dorsal sheath pressed against the inner sur- 

 face of the axial lobe along its middle portion, but diverging from it at the sides. The 

 section of the canal is oval, nearly twice as wide as high, but it is obviously somewhat de- 

 pressed. The original canal evidently filled nearly the whole of the dorsal part of the glabella 

 in this particular region. Unfortunately, the connection with the mouth is not shown, and 

 the form of the hypostoma indicates that the section cut the glabella diagonally, either in 

 the anterior or posterior part, probably the latter. In all these cases it should be remem- 

 bered that the specimens were found lying on their backs, and the canal has fallen in (dor- 

 sally) since death. 



The sections show that in Ceraurus pleurcxanihemus the anterior part of the alimentary 

 canal was large, filling the part of the glabella below the heart; that the body cavity was 

 provided with a chitinous dorsal sheath extending back into the thorax; and that the pos- 

 terior portion of the mesenteron was likewise large and oval in section. Since the alimen- 

 tary canal must be connected with the mouth and anus, some such restoration as that of 

 Jaekel is indicated. No chitinous lining of the stomodjeum or proctodasum was found, but 

 it is not certain that any of the sections cut either of those regions. 



Calymene senaria. 



Ten transverse sections and one longitudinal slice show the form of the alimentary canal 

 in Calymene. One of these has been figured by Walcott (1881, pi. I, fig. 9) but without 

 showing the organ in question. 



The only section cutting the cephalon which shows any trace of the canal is a longi- 

 tudinal one (No. 141), which is not very satisfactory. It has a large, nearly circular, 

 opaque spot under the anterior part of the glabella which may or may not represent a sec- 

 tion across the anterior end of the mesenteron. Three sections (No. 9, 115, 143) show 

 the dorsal sheath, the latter having the mud-filled canal beneath it. The sheath arches 

 across the axial lobe as in Ceraurus, leaving room for the dorsal muscles at the sides and 

 above it. In this region the canal is large and oval in section. Six slices cut the mesen- 

 teron behind the abdominal sheath (Nos. 39, 117, 148, 153, 62, 65) (see fig. 23). In the 

 first four of these it is oval in section and large, but not so large as in No. 143. In the 

 last two, it is small and circular in section, from which it is inferred that the canal tapers 

 posteriorly. 



Cryptolithus goldfussi (Barrande). 



Illustrated: Beyrich, Untersuch. iiber Trilobiten, Berlin, 1846, pi. 4, fig. ic. Barrande, Syst. Sil. Boheme, 

 vol. I 1852, pi. 30, figs. 38, 39. 



Both Beyrich and Barrande have shown that from the posterior end of the axial lobe 

 to the neck-ring on the cephalon, the alimentary canal in Cryptolithus has a nearly uniform 

 diameter of less than half the width of the axial lobe. In front of the neck-ring, it enlarges, 

 and while its original describers state that it extends only about halfway to the front of 



