I46 NEW YORK STATE MUSEUM 



lateral eyes, is therefore probably correct, for we find not only 

 traces of the eyes, 1 as he was aware, but also of the suture lines. 



In studying our material of Cryptolithus tesselatus 

 (Trinucleus concentricus) we had occasion to ob- 

 serve still a further suture, which, to our knowledge, has hitherto 

 been neither figured nor described. This is shown in plate 35, 

 figure 7. It is as a rule but very faintly seen where the integument 

 is preserved, but remarkably sharp, as a raised line, on the interior 

 casts of the glabella in the Trenton limestone material. There it 

 has all the characters of a suture. It begins at a small node in front 

 of the median eye tubercle. This minute anterior node (see pi. 

 35, figs. 1-4, at a), which is connected with the eye tubercle 

 by a narrow crest, often also visible exteriorly, may possibly be 

 another ocellus, either accessory to the first, or representing the 

 second pair of median ocelli occurring originally in crustaceans and 

 arachnids in a much reduced form. 



From the anterior tubercle the suture extends over the anterior 

 portion of the frontal lobe of the glabella in two diverging lines to 

 the antero-lateral corners of the glabella, where it recurves 

 abruptly, then following the lateral grooves to near the first 

 glabellar furrows, where it disappears. We have seen this suture 

 in so many specimens that there can be no doubt of its distinct 

 actuality. The area between the lines is often set off from the rest 

 of the glabella in being a little less convex. In front this triangular 

 area is separated from the brim by an abrupt break. 



We see in this triangular area the rostral piece or epistoma found 

 in many trilobites in front of the hypostoma and separated from 

 the cephalon by the facial suture. In Cryptolithus, we believe, it 

 became incorporated, or rather was drawn up into the glabella by 

 two factors ; the exceptional swelling of the frontal lobe of the 

 glabella and the development of the broad brim. Both peculiar 

 characters of the genus are obviously connected with its adaptation 

 to a mud-groveling life, which also led to the loss of the lateral 



1 It is worthy of notice in this conection that the State Museum contains 

 specimens of Eodiscus (Microdiscus auct.) speciosus, which 

 also show rudimentary eye tubercles on the cheeks, thereby indicating that 

 also this genus of the Agnostidae had, owing to a special adaptation to living 

 in the bottom mud, its lateral eyes reduced to faint rudiments and therewith 

 lost the facial sutures. The position of the rudimentary eyes indicates that 

 this genus also could not belong to the Hypoparia, and it further corroborates 

 Jaekel's view that the Agnostidae are not very primitive trilobites as generally 

 supposed, but highly specialized types. 



