174 C. E. Beecher — Ventral Integument of Trilobites. 



Plate V. 



Figure 1. — Ptychoparia striata Emmr, Dorsal view of the anterior portion 

 of a specimen preserved as a cast in sandstone, and enlarged 

 about two diameters. In the glabellar and anterior thoracic 

 region, the filling of the body cavity has been removed from the 

 axial region, thus exposing the imprint of the hypostoma and 

 ventral integument with its buttresses, or apodemal structures. 

 Eeduced from the original figure published by Jaekel. 



Cambrian, Bohemia. 



Figure 2. — A specimen of Triarthrus Becki Green; viewed from the ventral 

 side. The appendages have been removed and the ventral mem- 

 brane exposed. In the glabellar region are seen the hypostoma 

 and just below it the semicircular convex metastoma with side 

 lappets. Below, in the axial region, the buttresses and thicken- 

 ings of the sternal arches are clearly marked, as described in 

 the text. Enlarged about nine diameters. 



Figure 3. — The same specimen enlarged only a little more than three diam- 

 eters. The illumination is from the side opposite to that in the 

 preceding figure. 



Figure 4. — Triarthrus Becki Green. The ventral side of the middle thoracic 

 region of the specimen illustrated on Plate IV ; showing the 

 ends of the pleurotergites on the outside, with the joints of the 

 endopodites within the pleural regions, and the gnathobases 

 extending obliquely inward in the axis. The sternal arches 

 with their longitudinal ridges and the interarticular membranes 

 are represented. Enlarged four and one-fourth diameters. The 

 extensions of the limbs beyond the carapace are omitted. 



Figure 5. — Asaphus megistusljocke. A reduced outline of the figure pub- 

 lished by Mickleborough ; 9 showing the endopodites in the 

 pleural areas, with the gnathobases 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. 



Figure 6. — An enlarged profile of the mesosternal ridges of the preceding ; 

 from a sketch furnished the writer by Schuchert. The lower 

 represents the ventral aspect. 



Figure 7. — Transverse section through the thoracic region of Calymmene 

 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. 



