212 NEW YORK STATE MUSEUM 



tonguelike extension bent more or less downward, it was then argued 

 (op. cit., p. 420) that this was probably not the normal position of 

 the lobe. 



The carapace of Mixopterus multispinosus, however, 

 exhibits a niunber of features that seem to suggest a different orienta- 

 tion of the process, in this species at least. The tonguelike process 

 is separated from the carapace by a ridge that is in line with the 

 frontal margin of the carapace and it is surrounded by a suture. Its 

 straight frontal and curved lateral margins give the appearance of a 

 lobe cut off, or rather fitting into the marginal shield of the ventral 

 surface of the carapace, and indeed, the specimen, plate i, figure 3, 

 shows at a rounded, protruding lobes of the marginal shield which 

 snugly fit into the sides of the frontal process. Moreover, the 

 frontal margin of the carapace is not straight transversal as the 

 trapezoidal outline would have one expect, but is curved outward in 

 front of the eyes, and this curved outline is continued backward into 

 oblique folds that pass to the postero-lateral corners of the carapace. 

 These folds, together with the preocular projections delimit, however, 

 a perfectly triangular carapace of a typical Eusarus (see diagram, 

 plate I, figure 4). One can therefore not help feeling that the 

 narrow segments (6 of diagram) at the antero-lateral corners, which 

 give the carapace in the specimen a trapezoidal outline, are also parts 

 of the head-shield, that were originally bent downward under the 

 shield, and only became flattened out when the ventral integument 

 of the cephalothorax separated from the carapace along the lateral 

 suture, perhaps in moulting. In the specimen, here figured, it is 

 proved to have become separated by having become subsequently 

 displaced and pushed forward of the carapace. 



As in Eusarcus vaningeni, concentric wrinkles upon 

 the middle portion of the carapace indicate that this part was con- 

 siderably elevated and therefore likely to have steeply inclined cheeks 

 with reversed curvature in the lower part. 



We arrive thus at a structure of the ventral side, corresponding 

 to that observed in Hughmilleria (see Clarke and Ruedemann, p. 428) 

 where an epistoma and two fianking antelateral shields have been 

 observed as integral parts of the marginal shield of the ventral side. 

 In that genus, however, these plates have become separated by 

 sutures from the carapace and the remainder of the ventral integu- 

 ment. 



Worthy of special notice is the clasping organ of the male (see 

 plate I, figure 3) observed attached to the first endognathite in the 

 most complete specimen. It appears as a fairly large (3 mm long) 



