BUBBLE-HEADED TRILOBITES, AND A NEW OLENID EXAMPLE

Several trilobites developed an inflated cephalic lobe with a distinct ive bubble-like profile. This happened polyphyletically in at least se ven families ranging from the Cambrian to the Silurian. We describe a new species of Ordovician (Tremadoc) olenid trilobite, Parabolinella b olbifrons, having this morphology. A review of other trilobites with a pparently similar cephala shows that the bubble-headed appearance was derived in several different ways and probably acquired different func tions. In deiphonine cheirurids, staurocephalids and Paraphillipsinell a all, or only the frontal part of the glabella, is involved in the in flation. These species have rigidly attached conterminant hypostomes, and glabellar inflation may have matched a comparable inflation of the stomach. In the new species, as in several Cambrian examples with nat ant hypostomes, inflation is confined to a median area of the preglabe llar field. This is unlikely to have involved any modification of the alimentary system.