126 NEW YORK STATE MUSEUM 



Dalmanites perceensis nov. 



Plate 4, figures 1-3, plate 5, figure 2 



The parts found of this species are separated pygidia and cranidia. In 

 the latter the frontal lobe is gently rounded and depressed ; the first and 

 second lateral lobes well fused at their extremities ; the surface of the 

 frontal lobe coarsely papillose. The pygidium is broadly triangular, but 

 little arched at the sides, the lateral margins rounding in full curves and 

 the tail spine short, acute and upturned ; the axis has straight regularly 

 converging dorsal furrows and its width is less than two thirds the width of 

 each pleura. It bears 18-20 broad flat directly transverse annulations with 

 very narrow furrows. The fourth and eighth annulations bear two strong 

 nodes on the axis and others on the ninth, twelfth and thirteenth show 

 fainter traces of them. The broad and flat pleurae bear 15-17 flat ribs 

 grooved by narrow and sharply incised oblique furrows ; the ribs bend 

 abruptly backward near the margin and are discernible almost to the edge 

 of the shield. They are also sparsely but very irregularly nodose, the nodes 

 being large and coarse. The whole surface is finely granular. 



The dimensions of this species are impressive. A cranidium measures 

 from the occipital ring to the anterior suture 70 mm and across the frontal 

 lobe 60 mm, corresponding to an entire animal, having a length of about 1 1 

 inches. One entire pygidium measures 102 mm in length and 144 mm 

 across the anterior margin. This, however, does not express the full size 

 attained by the creature. 



Among the imperfect pygidia is one retaining a part of the axis and of 

 one pleura. The 6th axial segment from the top of the specimen (it is not 

 clear that this is the upper margin of the pygidium) has a length (width) of 

 35 mm. Comparison with other pygidia of this species shows that a shield 

 with a length of 25 mm has a 6th axial segment 5.5 mm long and in this 

 proportion the length of the large pygidium would have been 159 mm or 

 6^ inches. Considering the relation of the parts in species of this type we 

 find that a pygidial length oi 6% inches implies a total length of about 25 

 inches. This would be by far the largest Dalmanites yet recorded. The 

 writer has noted the great size attained by another species of this genus 

 Dal. (Coronura) myrmecophorus Green from the Onondaga 

 limestone of the Appalachian gulf [Pal. N. Y. v. 7, pi. 15] and a restoration 

 from a large pygidium gave a total length of 16^ inches. This restoration 

 Avas made with due consideration to variation in proportion of the parts in 

 the various groups of the genus in both Coronura and Probolium, the 

 cephalon being relatively short. If these figures indicating the size 

 attained by Dalmanites perceensis are approximate there is but 

 one trilobite known whose parts indicate still larger proportions, the mag- 



