. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 316 FIELDIANA: GEOLOGY, VOLUME 13 cep), lies between the lateral epitega, and extends from the rostral epitegum to the posterior border. A pineal macula (figs. 91,124, pm) is usually marked by its ridge pattern and a prominence, but there is no foramen. There is sometimes a distinct postrostral field ( Fig. 92. AUocryptaspis laticostata, CNHM, PF 1811; ventral side of incom- plete rostrum, showing maxillary brim, mxb (X 3). 112,A, prf) (Stensio, 1958, pp. 299-300 = pineal triangle of Denison, 1963
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 316 FIELDIANA: GEOLOGY, VOLUME 13 cep), lies between the lateral epitega, and extends from the rostral epitegum to the posterior border. A pineal macula (figs. 91,124, pm) is usually marked by its ridge pattern and a prominence, but there is no foramen. There is sometimes a distinct postrostral field ( Fig. 92. AUocryptaspis laticostata, CNHM, PF 1811; ventral side of incom- plete rostrum, showing maxillary brim, mxb (X 3). 112,A, prf) (Stensio, 1958, pp. 299-300 = pineal triangle of Denison, 1963), including the pineal macula posteriorly, and expanding for- ward to its meeting with the rostral epitegum; this may not be a distinct epitegum, but only a part of the central epitegum that is demarked by the supraorbital sensory canals. Except in Ctenaspis, the surface of the shield is covered with den- tine ridges, sometimes elongate, and at other times broken into short lengths or denticles. The ridges are arranged according to a pattern that is taxonomically important in general, though it may be variable in detail. In some genera the ridges are arranged in scale-like areas that presumably represent fused scales of an ancestral condition. The fineness of the ridges is also of taxonomic importance, and has been represented as the number of ridges per millimeter. This is usually measured in the central part of the dorsal shield; near the lateral borders the ridges are usually finer, and on the ventral shield they are usually slightly coarser. In a few cyathaspids there are coarser and higher ridges separated by a number of lower and finer ridges. Dentine ridges also cover the maxillary brim, usually ar- ranged parallel to the anterior edge, though they have an antero- posterior arrangement in AUocryptaspis laticostata (fig. 92). The crests of the ridges may be flat, or roundly or angularly convex, and tend to be higher and sharper near the lateral borders, especially. Pleas
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