CALYMENE AND CERAURUS. 5 l 



shown as a thickened, probably chitinous sheet thrown into low sharply crested folds equal 

 in number to, and pointing in a direction just the reverse of, the crests of the segments 

 of the thorax. Under the pygidium, where there would of course be less wrinkling, the 

 folds are hardly noticeable. In the actual specimens one sees more plainly than in the 

 figures the line of separation between the ventral membrane and the appendages, but the state 

 of preservation of everything beneath the dorsal shell is so indefinite that one does not feel 

 sure just what the connection between the appendages and the membrane was. In the origi- 

 nal of figure 5, plate 2, which seems to have been cut so as to cross tlie appendages at their 

 line of junction with the ventral membrane, there appear to be narrow chitinous (?) plates 

 extending from the ventral membrane to the dorsal test. 



Appcndifers. 



In Ceraurus there are regular calcareous processes which extend down from the dor- 

 sal test just inside the line of the dorsal furrow, and which undoubtedly serve as points 

 of attachment of the appendages. These processes, which for convenience I have desig- 

 nated as "appendifers," are broken off in most specimens showing the lower surface of 

 Ceraurus pleurexanthemus, but on certain ones cleaned with potash they are well preserved. 

 Doctor Walcott showed them well in his figures of the lower surface of this species (1875, 

 pi. ii ; 1881, pi. 4, fig. 5), while the attempt of Raymond and Barton (1913, pf. 2, fig. 7) 

 to show them by photography was not so successful. 



There is one pair of appendifers on each of the thoracic segments and four pairs on 

 the pygidium. On the cephalon there is one pair under the neck furrow, and a pair under 

 the posterior glabellar furrows. These are not concealed by the hypostoma. Further for- 

 ward, and completely covered by the hypostoma, are two much less strongly developed but 

 similar ones, so that there are in all four pairs of appendifers on the cephalon, though it 

 is extremely doubtful if the appendages were articulated directly to all of them. On a 

 specimen of Ceraurus pleurexanthemus 30 mm. long on the median line, the dorsal furrows 

 are 7.5 mm. apart at the anterior end of the thorax, and the tips of the appendifers of 

 this segment are only 4 mm. apart. Each consists of a straight slender rod with a knob- 

 like end projecting directly downward from the dorsal test, and supported by a thin cal- 

 careous plate which runs diagonally forward to the anterior edge of the segment directly 

 under the dorsal furrow. On the pygidium three pairs of the appendifers have this form, 

 while the fourth pair consist of low rounded tubercles which are concealed by the doublure. 

 These appendifers are probably cut in many of Walcott's sections of Ceraurus, but owing 

 to the state of preservation it is not always possible to determine what part is appendage, 

 what part is body cavity, and what part is appendifer. 



Nearly forty years ago Von Koenen (1880, p. 431, pi. 8, figs. 9, 10) described 

 and figured the appendifers of Phacops latifrons. He found them to be calcareous pro- 

 jections on the hinder margin of each segment, converging inward, and about 1.5 mm. long. 

 He correctly considered them as supports (Stiitzpunkte) for the feet. 



Appendifers are well developed also in Pliomerops, and in well preserved specimens 

 of Calymene senaria from Trenton Falls they are present, but instead of being rod-like 

 processes, they are rather thick, prominent folds of the shell. They are also well shown 

 in some of the thin sections. A specimen of Triarthr.its (No. 229, our pi. 5, fig. 2) has 

 broad processes extending downward from the lower side of the test below the dorsal 

 furrows, much as in Calymene, and the individual of Cryptolithus shown in plate 8, figure 



