Indications of Cephalic Sutures in Trinucleidæ and Harpedidæ

Abstract

RUDOLF RUEDEMANN¹ in 1916 summarized the available evidence regarding traces of cephalic sutures in Trinucleidæ, Raphiophoridæ, Dionididæ, and Harpedidæ. The well-known marginal sutures in the first and last families he considered as secondary acquisitions. They are generally regarded as having facilitated ecdysis; but specimens are rarely found which have fractured along them. One might even draw a comparison between the marginal suture, which is nearer the dorsal than the marginal side of the brim, and the subcranial furrow of Phacops (s.s.). Ruedemann‘s reconstruction, especially of the anterior facial suture, from traces on internal moulds, is so interesting in the case of Cryptolithus tesselatus Green, in spite of P. E. Raymond‘s treatment² of the lateral eye-lines as genal cæca and not lateral parts of a facial suture, that for a number of years a look-out has been kept for corresponding evidence on the eastern side of the Atlantic.