574 Contributions to Invertebrate Palaeontology. 



irregularly folded together in such a manner as to be diflBcult of 

 interpretation. The several plates vary considerably in form among 

 themselves, and probabh'^ represent those from different parts of the 

 bod}'. 



Tlio general form of tlie plates is triangular, Trith the apex, or initial point 

 of growtli, a little inclined to one side ; the hase, or margin of accretion, is 

 usually the longest side, but not in all cases. One set of plates has the shorter 

 sides diverging at nearly right angles. On this form, the basal line is convex 

 for more than two-thirds its length, and concave on the remaining portion, 

 giving a sigmoidal outline ; of the shorter sides, one is straight to near the 

 apex, where it becomes rounded, and the other is slightly concave. Another 

 form has the shorter sides diverging at an angle of about 105 degrees, one 

 slightly convex and the other concave ; while the basal margin is convex in 

 two sections, with a constriction or interruption between the two sections, or 

 at about one-third of its length from the straight margin. The plates of this 

 and tl>e preceding form have the surface regularly annulated transversely, 

 parallel to the basal margin, the annulations very fine, and regiiLirly increas- 

 ing in size and strength from the apex to the base, except in aged specimens, 

 where they are again crowded near the border : five undulations may be counted 

 in an eighth of an inch where strongest. These forms, also, have the straight 

 margin often fractured and bent, as if they had been broken along that side ; 

 indicating tliat two such plates may have been united along this line ; and on 

 the only individual showing several plates together, this would appear to be 

 the case. A third form of plate is narrowly triangular or conical, the basal 

 border being the shortest, and simply convex ; the other sides being slightly 

 curved throughout, but more distinctly so near the apex, which is obtusely 

 rounded; the lateral margins are of unequal length, and the annulations of 

 the surface finer and more closely arranged than on the other forms. 



The individual specimens are much too few in number to give 

 any very satisfactory idea of the general form of the complete body, 

 or of the number of ranges of plates of which it may have been 

 composed. There appears to be no reason, however, to doubt the 

 correctness of the reference of these plates to the genus Phimalites 

 Barrande, as their general form and surface structure are exactly 

 like those given by Dr. Barrande, and also to those given in Vol. II, 

 Pal. Ohio, pi. 4, figs. 1 and 2 (P. Jamesi), as occurring in the rocks 

 of the Hudson River group, at Cincinnati; while some idea may 

 be obtained of the probable form of the entire body from the out- 

 line figure of a European .species, represented in fig. 3 of the same 

 plate. These Devonian specimens, however, have been of very 

 much greater size than the above, as the plates here figured are all 

 represented of natural size, the larger individual plates being more 



