104 G. F. MATTHEW: ILLUSTRATIONS OF 



ADDITIONAL FEATURES OP THE CEPHALIC SHIELD. 



This is the only part of the auimal described by Prof. Hartt, and though his account 

 is very fiill and accurate, it does not give all the characters of this part of the body. 

 It is seldom that the head is found "more than twice as wide as long," except when 

 flattened by pressure in the slate ; and the anterior margin is i^erceptibly angulated where 

 the lateral thirds begin. It may be said also that the fold, though weak at the sides, goes 

 entirely round the posterior angle. Prof Hartt does not mention a pair of spines, or 

 tubercles, which are set in the hollow between the cheek and the glabella, on the edge of 

 the posterior marginal furrow (one s^jine being at the inner corner of each cheek) and 

 which can be seen in almost all stages of growth of this species. The statement that the 

 glabella is longer than its width applies to the younger tests ; but in the adult, as pre- 

 served in the slates, it is more frequently wider than its length, and may be generally 

 described as being as wide as it is long. The ocular ridge, and the lines that diverge 

 from it toward the anterior margin {Fig. 10), are much more distinct on the inner, than on 

 the outer, surface of the shield ; and the lines not only bifurcate, but are found to anasto- 

 mose with each other, forming a reticulated ornamentation over the inner surface of the 

 anterior part of the head. Many of the spines that decorate the front of the cheeks are set 

 at the intersections of these lines. The spines are spoken o£ as being " sparsely sown ;" 

 but this remark does not apply to all varieties of the species, as will be seen further on.* 

 The example of this species figured in " Acadian G-eology " is considerably below the full 

 size of the adult, the head of which, as it occurs flattened in the slates, averages 19 by 38 

 mm., but is occasionally seen as large as 20 by 40 mm. 



GENAL SPINES. (Fig. 8.) 



Among the parts not described by Prof. Hartt are the genal spines. These appendages 

 are occasionally found attached to the under side of the anterior marginal fold, and, when 

 detached, carry with them the lower half of the lateral third of this fold. They are not 

 spinous like the surface of the cephalic shield, but they sometimes have a few scattered 

 tubercles, and are covered with minute granulations, visible with a lens. The spine in 

 the adult, forms two-fifths of the whole length of the detached cheek-piece, and is moder- 

 ately incurved to the point ; the spine narrows rapidly in the first third, and is sharp at 

 the extremity ; a faint rib traverses the cheek-piece along the median line. 



FACIAL SUTURE. 



Prof. Hartt makes no allusion to this feature of the test in his description of the spe* 

 cies, and, if the spines were not found attached, its position would hardly be suspected. 

 In its course along the upper surface of the test it agrees exactly with that of Conocori/phe 

 Sulzeri, but differs on the under surface. In C. Sulzeri and Cl. coronatus, it begins at one- 

 eighth of the distance from the apex of the shield, but in our species at about one-third of 



' There appears to be a misprint in this part of the description in "Acadian Geology," p. 648, line 22, where the 

 spines are said to be always wanting "on the cheek lobes," perhaps (in the furrows) "around the cheek lobes" is 

 intended. 



