The Fauna of the St. John Group. 359 



resemble the adult in Ellipsocephalus and Agraulos.* The 

 ocular fillet in these minute head shields appears close to 

 the anterior margin, as in the Conocorypheans, but the 

 development of the anterior limb of the cheeks in the later 

 stages pushes it backward. In the advanced position of the 

 ocular fillet, as well as in the long and prominent glabella 

 in these little tests, we are again reminded of Ellipsoce- 

 phalus, but a counterpart of the straight facial suture and 

 the short eyelobe, comparatively distant from the posterior 

 margin, is to be found in Agraulos, rather than Ellipsoce- 

 phalus. 



The form of the anterior margin in these young tests 

 exhibits affinities in another direction, for in the depressed 

 front, with narrow, sharp, threadlike marginal fold, which 

 appears at this stage of growth, there is a counterpart to the 

 same portion of the shield in the adult of Liostracus and 

 Solenopleura. 



The two genera last named with Ptychoparia exhibit an 

 important departure from the primitive type in the with- 

 drawal, during growth, of the eyelobe from the vicinity of 

 the lateral margin, of the shield toward the side of the 

 glabella. From this position of the eyelobe results an ex- 

 tension of the posterior margin of the middle piece of the 

 headshield, a character which is most pronounced in the 

 species of pelagic habits, and which extension is accom- 

 panied by a corresponding prolongation of the pleura?. 



Another change which occurs during growth, namely, 

 the contraction or shortening of the eyelobe, is one which, 

 among the genera under review, is most obvious in Soleno- 

 pleura; and this genus stands out from the others also in 

 the inflation or enlargement of the cheeks at the expense 

 of the glabella, and in the ornamentation of the test by 

 tubercles and granulations. 



These three peculiarities of certain of these early trilo- 

 bites, viz., the withdrawal of the eyelobe towards the 



* The references herein to the standing of Agraulos relate to the 

 species which are near in form to the type, but there is a species in 

 the lower part of Div. I. which combines the characters of this 

 genus with those of Ellipsocephalus. 



