Cryptolithus tessellatus Green.
Specimen No. 233 ([pl. 7, fig. 1]; text [fig. 45]).
This is the best preserved entire specimen. It is developed from the lower side, and shows the hypostoma, antennules, and a few fragmentary appendages of the cephalon, the outer portions of the exopodites of thorax and pygidium on both sides, and the endopodites on the left side.
The hypostoma is imperfectly preserved and is turned completely around, so that the anterior margin is directed backward, and the posterior one is so much in the shadow that it does not show well in any of the photographs. The form is, however, essentially like that of Trinucleoides reussi (Barrande), the only other trinucleid of which the hypostoma is known, except that the border does not extend so far forward along the sides, and it is much smaller.
The antennules are not inserted close to the hypostoma, as in Triarthrus, but at some distance from it, and, as nearly as can be determined, directly beneath the antennal pits which are seen near the front of the glabella in many species of trinucleids.
Fig. 45.—Cryptolithus tessellatus Green. Drawing of specimen 233, made by Professor Beecher. × 9. Below are parts of two of the endopodites of specimen 236, showing the interarticular membranes. × 41.
The antennules are long, and are composed of far fewer and longer segments than those of Triarthrus. In this specimen they converge backward, cross each other and at the distal end are more or less intertwined.
As is shown in the drawing and photograph, very little can be learned from this individual about the other appendages of the cephalon. A few fragments of exopodites on either side suggest that these members pointed forward and were much like those in Triarthrus, but nothing conclusive is shown.