Trilobites during this period sank to a very subordinate position, but Ostracods (Cythere, Kirkbya, Beyrichia) were abundant.
Crustacea occupied an extremely prominent place; there were Phyllocarids such as Hymenocaris, and Ostracods like Entomidella; but by far the most important in numbers and development were the Trilo bites, now extinct, but in palaeozoic times so abundant.
In a few Entomostraca (some Phyllopoda and Ostracoda) the chitinous lining of the fore-gut develops spines and hairs which help to triturate and strain the food, and among the Ostracods there is occasionally (Bairdia) a more elaborate armature of toothed plates moved by muscles.
Also, I found some ostracods, about 1½ millimeter long.
Content Emphasis is placed on both marine and non-marine ostracods and their application to Quaternary research.