ART. 27 Is^EW MIDDLE CAMBRIAlsr FOSSILS EUEDEMANN' 15 



developed into gills as in the classic Triarthriis hecJci. In contrast 

 to this the adjoining figure shows the thoracic feet stripped of the 

 endopodites, and therefore looking like cephalic appendages. Some of 

 Walcott's drawings (pi. 25, fig. 6, and pi. 26, figs. 2-4) also show 

 cephalic feet with gills. Where Walcott figures antennae, mandibles, 

 maxillulae, and maxillae (pi. 25, fig. 1, and pi. 26, figs. 1 and 5), 

 the posterior margin of the cephalon, as shown before, is mistaken 

 for the mandible, and the cephalic feet, which have lost their endop- 

 odites by poor preservation, for maxillulae and maxillae. This mis- 

 conception led Raymond (1920, p. 116, fig. 32) to an erroneous restora- 

 tion of Marrella sinlendens^ showing five pairs of uniramous cephalic 

 appendages, and to the statement {ihid., p. 143) that Marrella forms 

 " an intermediate stage between the Trilobita and the higher 

 Crustaceae." 



Plate 7, Figure 1, gives a ventral view, exhibiting the frontal 

 doublure and the hypostoma. The transversal suture just behind 

 the frontal margin appears to represent the frontal portion of the 

 uniting facial sutures, with a rostral plate posteriorly to it. The 

 most distinctive feature is the presence of white strands of connective 

 tissue extending sideways from the anterior margin of the oval hy- 

 postoma into the frontal thickened margins of the free cheeks. 

 Behind the glabella a portion of the intestine is seen, and behind 

 this the internal view of the axial lobe of the thorax. The lower 

 half of the picture shows more clearly the crowded, partly over- 

 lapping joints (segments of Raymond) of the posterior portion 

 of the thorax. 



Plate 7, Figure 2, is important in shedding light on the charac- 

 ter of the supposed " large crescentif orm sessile ej^es," which " occur 

 on the anterior margin just within the base of the anterior spines." 

 (See Walcott's pi. 25, figs. 4 and 5.) Raymond speaks (p. 115) 

 of " large marginal sessile eyes." Figures 3 and 4, which are fur- 

 ther enlargements of the " eyes " in Walcott's Figures 4 and 5, show 

 these bodies to be really circular to oval in outline. In both speci- 

 mens they are squeezed out of place with respect to the thin test 

 of the carapace, in the original of Figure 3 laterally and in that 

 of Figure 4 anteriorly, both specimens showing oblique compres- 

 sion by their general outlines. In Figure 4 a triangular patch of 

 the test adhering to the gland on the right and in Figure 3 the gland 

 on the right (partly cut) are distinctly integral parts of the test. 

 In Figure 2 they are in their normal position, which is under the 

 cephalon at both sides of the glabella. This location, as well as 

 their outline, the indications of their composition of concentric or 

 spiral ducts (as seen especially in fig. 3), and their prominence di- 

 rectly after the molting suggest their nature as shell glands rather 

 than as digestive glands or hepatic ceca. It is quite probable that 



