I l6 WILLIAM PATTEN. 



ventral direction. Its anterior end lies back of the cervical suture 

 and from there it extends backwards about two thirds the length 

 of the post-cephalic portion of the buckler. It is readily recog- 

 nized by its fine, soft matrix and the concentric black lines, each 

 line clearly and sharply defined and separated from the adjacent 

 ones by regular intervals. The lines are similar in color and 

 thickness to those made by the skin when seen in section. The 

 whole structure, while puzzling, is unquestionably produced by 

 some organic structure, not by sedimentation within an irregular 

 cavity, or by mud accumulated within the alimentary canal. The 

 anterior boundaries of the black lines are ill defined, but the pos- 

 terior ones often form distinct loops as though the whole struc- 

 ture consisted of a series of broad lamellae wrapped around a 

 central axis, and with free, more or less separated, posterior mar- 

 gins. In some cases the whole mass of lamellae is much distorted, 

 or they may protrude from some rupture in the walls of the 

 crushed shield. Under these conditions they still preserve their 

 essential characters, showing that while originally soft and flexible 

 they had at least as much firmness as the skin of the trunk. Be- 

 hind the laminated portion, the soft matrix extends in an irregular 

 undefined and structureless mass toward the cloaca. The remain- 

 ing space within the buckler may be filled with a coarser matrix 

 similar to that in which the whole animal is imbedded. 



On the dorsal side of the laminated body, there are usually 

 scattered fibrous masses, and one or more irregular, undefined 

 bony plates, apparently attached by vertical sheets of blackened 

 tissue to a low median ridge on the inner surface of the anterior 

 median dorsal. Anteriorly, this ridge deepens into a prominent 

 hollow process directed downwards and forwards toward the 

 thickest part of the covering on the laminated core, Fig. 2. 



Several specimens have been found with the mouth parts in 

 their natural position, held there by membranes, whose contours 

 can be determined with considerable accuracy. 



The oral region, Fig. 3, is covered by an undulating structure- 

 less membrane in which are imbedded the various oral plates. 

 The membrane is attached to the lateral and anterior margins of 

 the head, as far at least as the shoulder on the anterior border of 

 the mandibles. It extends backwards, underneath the anterior 



