Page:Walcott Cambrian Geology and Paleontology I.djvu/33

Rh Pygidium small, elongate, without defined segments.

.—Burlingia hectori, new species.

.—This genus is represented by a single species from the central portion of the Middle Cambrian fauna. The only form with which it can be directly compared is Schmalenseeia Moberg, which is represented by specimens of the cranidium, pygidium, and fragments of the thoracic segments belonging to a single species. The cranidium of Schmalenseeia differs in having a convex glabella divided into four lobes by four transverse furrows, and in the presence of a defined occipital segment. The fragments of the thorax illustrated by Dr. Moberg (1903, pl. IV) and his description of them indicate that the pleuræ were flattened and marked by shallow, direct furrows similar to those on the pleuræ of Burlingia. With the present information, it is in the pygidium that the great difference in the two genera is found. The pygidium of Schmalenseeia is large and it has a strong axial lobe divided into a number of segments; the pleural lobes are broad and marked by numerous backward-curving, flat furrows much like those of the thoracic segments of Burlingia. The pygidium of Burlingia is small and apparently without segments or pleural lobes; it is a simple plate as in Paradoxides.

Dr. Moberg (1903, p. 100) has noted the resemblance between the direction of the facial sutures of Schmalenseeia and those of some genera of the Cheiruridæ and Encrinuridæ, while the broad anterior margin of the head suggests some of the Conocoryphidæ; he concludes that these resemblances have little value, as the other parts of the shield differ so largely from the representatives of these genera. In this I agree with him. The two genera are unlike all other trilobites and form a family type by themselves.

The genus is named after Mr. Lancaster D. Burling, of the United States National Museum, who found the only three nearly entire specimens of this interesting trilobite.

Dorsal shield small; longitudinally broad oval; slightly convex. Cephalon one-fourth the length of the complete dorsal shield, semicircular in outline, with genal angles prolonged into short slender spines that scarcely extend beyond the extremity of the first or anterior thoracic segment; the posterior margin of the cephalon is nearly