Page 381 - Introduction to Paleobiology and The Fossil Record

368 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

(a) (b)

(c) (d) (e)

Figure 14.4 Vision in trilobites: (a) lateral view of a complete specimen of Cornuproetus,
Silurian, Bohemia (×4); (b) detail of the compound eye of Cornuproetus (×20); (c) holochroal
compound eye of Pricyclopyge, Ordovician, Bohemia (×6); (d) schizochroal compound eye of
Phacops, Devonian, Ohio (×4); and (e) schizochroal compound eye of Reedops, Devonian,
Bohemia (×5). (Courtesy of Euan Clarkson.)

The proetids were isopygous forms with
large glabellae and long hypostomes having
genal spines and large holochroal eyes. The
group ranged from the Lower Ordovician to
the Upper Permian. Proetus was a small form
proparian gonatoparian opisthoparian with a relatively large, infl ated and often
granular glabella, known from the Ordovi-
Figure 14.5 Facial sutures: the tracks of the cian to the Devonian. Phillipsia, one of the
proparian, gonatoparian and opisthoparian youngest members of the order, was a small
sutures. The lateral suture (not illustrated) isopygous genus with large crescent-shaped
follows the lateral margin of the cephalon. eyes and an opisthoparian suture.
The naraoids, including Naraoia itself and
Tegopelte, have often been included with the
trilobites. They were not calcifi ed and lacked
and Ceratopyge together with pelagic forms thoracic segments. The group was restricted
such as Cyclopyge and Remopleurides, and to the Middle Cambrian. Naraoia was fi rst
the stratigraphically important trinucleids described from the Burgess Shale as a bran-
such as Onnia, Cryptolithus and Tretaspis. chiopod crustacean, but it has only more