1915] The Ottawa Naturalist. 39 



diuni is convex, strongly lobed and withcMit a distinct marginal 

 furrow. Axial lobe intermarginal, convex and divided into 

 four annulations and an interior doublure by four distinct 

 transverse furrows; lateral lobes crossed by three main 

 furrows and two shorter ones, corresponding to the furrow on the 

 lateral lobe of the thoracic segments, thus otitlining the anchy- 

 losed segments in the pygidium; a fourth segment and the ter- 

 minal portion are also outlined by a faint ridge. Thorax un- 

 known. This is a very distinctly marked species allied to 

 Bathyurus armatus Billings." (4). 



Corda (1) was the author of the genus and the first to figure 

 Agraulos (in 1847) but his drawing is so inaccurate that one can 

 hardly recognize any similarity between it and the original type 

 described by him as .4. delphinocephalus . Later, Barrande (2) 

 gave an excellent description of the same species under the name 

 Arionelhis ceticephahts, declining to use Corda's generic name. 

 Barrande's figures are so accurate that the indices worked out 

 from these compare favorably, indeed very closely, with those 

 worked out on the actual specimens. Barrande does not appear 

 to have noticed the presence of eye-lines, a primitive aspect of 

 this species and of many other Cambrian trilobites. One has 

 but to compare the indices (38-64) to appreciate how widely 

 Corda's figure differs from those of Barrande. x-V drawing from 

 an actual specimen found in the type locality of Skrey, Bohemia, 

 is shown on the plate. Fig. 3. The first mention of ^4. sarato- 

 gensis was by Walcott (3) in 1879 when he listed it as Ptycho- 

 paria {A.) saratogensis. In his next paper (5) he referred the 

 species definitely to the genus Agraulos. A copy of his figure is 

 shown on the accompanying plate in Fig. 2. Walcott, (7) in 

 1912, figures another specimen of the same species showing a 

 strong circum glabellar ftirrow; glabellar furrows and ridge, as 

 shown in Fig. 1. Both of the varieties above described occur at 

 the same horizon at the Hoyt Quarry. Raymond, (8) in his 

 " Revision of the Species which have been referred to the genus 

 Bathyurus," took Agraulos saratogensis as his type of the new 

 genus Plethopeltis, as has been previously stated. 



The writer made a critical and comparative examination 

 of the features of the four types referred to above and has 

 recorded a summary of his observations in the accompanying 

 plate, which is to a large extent self-explanatory. Figures 1 and 

 2, representing the two variations of P. (A.) saratogensis are 

 drawn from specimens from the Hoyt Quarry. Figure 3 is 

 drawn from a specimen of Agraulos ceticephalus Barrande. 

 Figvire 4 represents Phethopeltis armatus (Billings). On the 

 right of the figures are arranged in order the chief characteristics 



