FAUNA OF THE ST. JOHN GROUP. 55 



extended iuto a short spine directed outward ; inner side of the cheek with an arched 

 border in front, emarginate for the eye, and very short behind the eye ; posterior side of 

 the cheek nearly straight, with an obsolete border fold. Facial suture arching forward 

 and inward from the eyelobe to the anterior margin, and directed backward from the 

 eyelobe to the posterior margin. 



Thorax with a broad and prominent rachis of about twelve (?) narrow segments, 

 rapidly narrowing in the posterior half Pleura shorter than the joints of the rachis, 

 crossed diagonally by a sharp narrow furrow ; extremity of the pleura pointed and 

 extended into a sharp spine, directed backward. 



Pygidium small, narrowly semicircular, having a prominent rachis and three joints ; 

 side lobes narrow, with two ribs, the whole encircled by a distinct border fold. 



Size. — Centre piece of the head, length, 3| mm. ; width, 7 mm. Movable cheek, 

 length, 6 mm. ; width, 2| mm. Pygidium, length, 1-^ mm. ; width, 2| mm. 



Horizon and Locality. — In calcareo-silicious layers in black shale of Div. 3 6 at Navy 

 Island, St. John Harbour. 



Var. (PI. XIII, fig. 11.) 



A variety with more distinct furrows on the glabella, wider front margin, and broader 

 occipital ring and posterior margin, is found with the preceding. 



Among Angelin's three species of Leptoplastus, L. ovatus is the one which most 

 resenables this species ; that species, however, has a series of spines along the rachis, and 

 has an extended dorsal suture behind the eyes, and thus differs from the Acadian species. 



CTENOPYaE, Linrs. 



In the black slates of the Bretonian Division (Div. 3) there are locally immense num- 

 bers of minute trilobites, which appear to represent in the economy of Nature the swarms 

 of Aguosti that are found in the fine shales of the Acadian Division (Div. 1), and were 

 there buried in the fine mud that entombed the Paradoxides. These trilobites, though so 

 small, are of higher organization than the Agnosti, if one may judge by the number and 

 complexity of the parts of which their skeletons were composed. 



We are almost wholly indebted to the Scandinavian geologists for the elucidation of 

 the structure and relationship of these little trilobite.s. First Augeliu, whose classification 

 has been alluded to under the genus Leptoplastus, and then Linnarsson took up the study 

 of these forms. The latter added a number of new species to the group, and instituted 

 the genus Ctenopyge, to contain the peculiar form C. ]iecten and others. Still later. Dr. 

 W. C. Brogger made a careful analysis of this group, and proposed to class it under one 

 generic title — Leptoplastus. "While not prepared thus to reduce the genera of Salter, 

 Angelin, Linnarsson and Phillips that are included in Brogger's genus, his generic 

 description is such an excellent digest of the characters of the group that it should be 

 presented here, as it serves as a basis on which to arrange the several genera. 



Leptoplastus, Angelin, as amended by Brogger to cover also the genera Eurycare, 

 Sphserophthalmus and Ctenopyge, is as follows : 



Body oblong ovate, distinctly trilobed lengthwise, covered with a smooth crust. 



