Page:Walcott Cambrian Geology and Paleontology I.djvu/32

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Dorsal shield small, elongate, broad oval in outline. Cephalon about one-fourth the length, transversely semicircular; genal angle acute or spinose; glabella with transverse lobes. Free cheeks small, separate. Facial sutures cut the margin in front of the genal angles, extend in to the posterior portion of the eye lobe and outward from the anterior portion to the antero-lateral margin of the cephalon. Eyes of medium size, clearly defined.

Thorax with fourteen segments in the one species preserving them; pleuræ with flat, straight furrows.

Pygidium large, with strong axis and pleural lobes, or small and with medium axis and pleural lobes.

.—Central portion of the Middle Cambrian to the Agnostus pisiformis zone of the Swedish Upper Cambrian.

.—This family includes the genera Burlingia and Schmalenseeia. The first is represented by entire specimens and the latter by the cephalon, fragments of the thorax, and entire pygidia. The facial sutures and free cheeks relate Burlingia to some forms of the Cheiruridæ, while the pygidium of Burlingia recalls the simple pygidium of Paradoxides, and the pygidium of Schmalenseeia recalls that of Amphion. The flat, straight furrowed pleuræ of the thorax of Burlingia recall the pleuræ of Olenoides. The assemblage of characters in Burlingia and Schmalenseeia clearly indicate a distinct family of the Proparia, more primitive than any other forms of that order.

Dorsal shield small, elongate, broadly oval. Cephalon semicircular; one-fourth the length of the entire shield; genal angles with spines; cranidium with anterior and posterior limbs that extend outward from the glabella to the outer margin; glabella slightly convex, with indications of lobes. Free cheeks subquadrangular, small. Facial sutures extend from in front of the genal angles inward to the eyes and then obliquely outward and forward, cutting the anterolateral margin. Eyes of medium size.

Thorax with fourteen segments; pleuræ with a flat, direct furrow; pleuræ extended into backward-curving, falcate extremities.