6 
William Patten. 
III. Descriptive Part. 
The General Shape of the Cephalic Shield of Tremataspis is so well shown by the figur¬ 
es, tbat it requires but little description. The model from which the figures were made ? 
was constructed in wax öfter some eiglit or ten specimens of T. Schmidti , some belonging 
to the Petersburg Academy and others to the Museum of Dartmouth College. In tliis species 
the liead is much flattened, and quite different from the strongly convex dorsal and ventral 
surfaces of certain undescribed specimens tliat probably represent a new species. When seen 
from above, the anterior end of the shield is somewhat pointed, with a sliglit angle, or 
slioulder, near each lateral opening. The marginal serrations begin a little in front of the 
posterior pair of lateral openings, gradually shifting tlieir position at the posterior end of 
the liead on to the dorsal surface of the cornua. In the région of the four tubercles, there is 
a gentle swelling of the dorsal shield, and in front of it a more pronounced one on which are 
situated the median eyes and the olfactory organs. 
The dorsal shield is flattened on the sides, and shelves off at a sharp angle on the 
margins, suggesting in cross sections at this point the cephalic shield of Limulus 
(PI. I. fig. 3.). 
The whole anterior end of the head bends sliglitly downwards and gradually merges 
into the ventral shield. 
The Margins of the Oral Region: On the under side of the head is a large space tliat 
we shall speak of as the oral région. It is normally occupied by numerous bony plates, but 
in most specimens the plates bave disappeared. The opening is surrounded in front and on 
both sides by a narrow irregulär rim, formed by the turned over margins of the dorsal 
shield. The rim, which forms an extremely important morphological feature, is very fragile 
and great care is required to expose it without destroying its contours. I hâve successfully 
exposed various parts of it in several instances, and hâve obtained important data which 
differ materially form those of Rohon, as shown in his restoration of this région. 
Beginning at the anterior end, PI. I. fig. 1. and PI. II. fig. 8. we find a low, beak-like flexure of 
the dorsal shield, culminating on either side in apolished, rounded tooth-like projection. In the 
