No. 436.] APPENDAGES OF TREMA TASPIS. 



227 



The structure, Figs. 1-3, was at first deeply imbedded in 

 the matrix leaving only a small part of the dorsal surface 

 exposed, from which the outer layers has been worn off, reveal- 

 ing the characteristic polygonal meshwork of the middle layer. 



After exposing the entire dorsal surface of the plate by 

 cautiously removing the matrix with fine needles, to insure 

 against accidents in the subsequent treatment, it was photo- 

 graphed and modeled in wax on a large scale. This proved to 

 be a wise precaution, as the extremely brittle and fragile plate, 

 in spite of the utmost precaution, was accidentally injured, in 

 one of the many occasions when it was being placed in position 

 for examination. After the dorsal surface had been thoroughly 

 studied, it was covered with hard balsam and fastened face 

 downwards to a glass slide. When the remaining matrix had 

 been removed and the balsam dissolved off, the completely iso- 

 lated plate could be examined from any desirable point of view. 

 The other plates to be described were treated in a similar 

 manner. 



When seen from what I consider to be the dorsal side, Fig. 3, 

 the distal joint of the appendage appears something like the 

 blade of a knife. It is about 2.5 mm. wide by 7.5 mm. long 

 and of a light yellowish brown color. A cross section would be 

 triangular, with the thickest part on what I assume to be the 

 median side, or that side which when the appendage was in place 

 was nearest the body. The opposite or lateral margin, especially 

 toward its posterior end, is thinned down to a rather sharp edge, 

 ornamented by a series of glistening headings or scallops. Fig. 

 3^. The six headings nearest the posterior end are the most 

 regular and they are readily seen from either surface. Toward 

 the anterior end of the lateral margin <>ne can distinguish five 

 or six more undulations, somewhat irregular in size and best 

 seen from the under surface, Fig. 1, b. Towards its anterior 

 end, the lateral margin becomes thicker and more rounded so 

 that cross sections of the appendages at that point would be 

 more oval in outline. The dorsal surface is rather full and 

 rounded at the anterior end, flattening out posteriorly where, 

 near the apex, it takes a rather sharp downward curve, Figs. 

 2 and 3, as though the point were slightly bent. Near the 



