NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 23 



Description. — Glabella divided by a broad transverse furrow into 

 anterior and posterior lobe ; lobation more marked in larger individ- 

 uals. Anterior lobe rounded, slightly narrower than posterior lobe; 

 the latter rising steeply and extended upward and backward beyond 

 the occipital ring ; whether this extension is rounded or pointed at the 

 extremity could not be determined, as this portion is incompletely 

 preserved. One pair of short lateral furrows is visible on the posterior 

 lobe. Occipital ring short (sag.), mostly masked in dorsal view by 

 the glabellar extension, directed inward and backward at the sides. 

 Cheeks strongly convex, in their posterolateral part overhanging the 

 border furrow. Border expanded medially and causing a slight median 

 inbend of the border furrow which here forms a depression by merg- 

 ing with the axial furrow ; border narrowing gradually toward the 

 genal angle. Posterior cephalic border poorly preserved. Surface of 

 test faintly reticulate ; lateral border with four or five pairs of low 

 tubercles. 



Pygidium tentatively referred to the species on account of similar 

 ornamentation with axis well defined by deep axial furrows, showing 

 about seven rings plus a terminal unsegmented section, almost 

 reaching border. The first three rings may have had a node. Anterior 

 border furrow deep and wide, with well-developed geniculation and 

 facet. Lateral and posterior border furrow and border narrow through- 

 out. Pleural regions unsegmented, very convex like the cheeks. 



Width of largest cephalon 9.5 mm; length of holotype cephalon 

 4.6 mm, width 5.6 mm. Length of largest pygidium 5.0 mm, width 

 6.0 mm. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — This species differs considerably from C. lobatus 

 in the shape of the glabella, divided by a broad transverse furrow 

 and with the rear lobe extended backward above the occipital ring. 

 However, the presence of one or more, shallow transglabellar fur- 

 rows is a feature present in species obviously congeneric with C. 

 lobatus, and even in the form agnostoides of this species which 

 Lochman (1956) showed to intergrade with the typical form. Calo- 

 discus Helena (Walcott) has a broad, very shallow transglabellar 

 furrow and a rearward extension of the glabella, although not as 

 pronounced as in the present species, and on the whole the cephala 

 of C. Helena and C. fissifrons are very similar. The pygidium of C. 

 Helena, however, differs considerably in the broad, paucisegmented 

 axis from any pygidium observed at the North Chatham locality. 



T.v/'^^.— Holotype: U.S.N.M. 146004. Paratypes: U.S.N.M. 

 146005. 



