24 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



several palaeontologists, who consider that epipodites are really present. Since I am not able 

 to convince myself that their conclusion is based upon sound evidence, I give here my own 

 interpretation. There is of course, no a priori reason why trilobites should not have had 

 epipodites. 



Specimen No. 58589. 



Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, pi. 45, fig. 2; Zittel-Eastman Text-book of 

 Paleontology, vol. I, 1913, fig. 1377; Smithson. Misc. Coll., vol. 67, 1918, pi. 18, fig. i; pi. 20, fig. I. 



This is one of the most important of the specimens, as it shows the coxopodites of 

 three thoracic limbs and the well preserved endopodites of six thoracic and five pairs of 

 pygidial appendages. 



The appendages are all shifted to the left till the articular socket of the coxopodite is. 

 about 8 mm. outside of its proper position. The endopodites extend a corresponding amount 

 beyond the edge of the dorsal test and are there so flattened that they are revealed as a 



Fig. 2. Neolcnus serratus (Rominger). A sketch of the coxopodites 

 and endopodites of two thoracic segments. Note notch for the reception 

 of the lower end of the appendifer. X 3- 



mere impression. The coxopodites, which are beneath the test, seem to have been somewhat 

 protected by it, and while hopelessly crushed, are not flattened, but rather conformed to the 

 ridges and grooves of the thorax. 



The coxopodite of the appendage of the last thoracic segment is best preserved. It is 

 rectangular, about one third as wide as long, with a slight notch in the posterior margin 

 near the outer end. The inner end is obliquely truncated and shows about ten sharp spines 

 which do not appear to be articulated to the segment, but rather to be direct outgrowths 

 from it. There are similar spines along the posterior margin, but only two or three of 

 what was probably once a continuous series are now preserved. On the opposite margin 

 of the coxopodite from the slight depression mentioned above, there is a slight convexity in 

 the outline, which is better shown and explained by the coxopodite just in front of this. 

 That basal segment has the same form as the one just described, but as its posterior margin 

 is for the greater part of its length pushed under the one behind it, the spines are not shown. 

 On the posterior margin, two-thirds of the length from the proximal end, there is a shallow 

 notch, and corresponding to it, a bulge on the anterior side. From analogy with Ceraurus 

 and Calymene it becomes plain that the notch and bulge represent the position of the socket 

 where the coxopodite articulated with the appendifer. Since these structures have not been 

 shown in previous illustrations, a drawing giving my interpretation of them is here inserted 



