This article deals with the occurence of boulders of Theciidae MILNE EDWARDSHAIME, 1849 (Tabulata), found in the Red Saalian Boulder Clay, in the northern part of the Netherlands. The boulders are mostly found in limy preservation. Until now five genera have been found, i.e. Thecia MILNE EDWARDS-HAIME, 1849; Angopora JONES, 1936; Romingerella AMSDEN, 1949; Fossoporaa ETHERIDGE, 1903 and Laceripora EICHWALD, 1854. KLAAMANN (1961, 1964) and STASINSKA (1967) described three species of Thecia, i.e. Th. swindereniiana (GOLDFUSS, 1829); Th. saaremica KLAAMANN, 1961 and Th. confluens (EICHWALD, 1854). OEKENTROP (1970) separated Th. expatiata LONSDALE, (1839) from Th. swindereniana (GOLDFUSS). Although a number of similarities exist, it still uncertain if Th. saaremica KLAAMANN is quite synonymous with Th. expatiata (LONDALE). STEL (in press) considers Th. expatiata and Th. saaremica as syynonyms of Th. swindereniana (GOLDFUSS). Two types of Thecia can be distuinguished among the boulders, i.e. a 'forma swindereniana' and a 'forma confluens'. The corallites of the 'swindereniana-types' clearly show the ontogenetical different stages of development, as stated by OEKENTORP (1970) and STEL (in press). Dependent on the ontogenetical stage, however, the number of septa varies remarkebly. In larger corallites (0,8-1,1 mm.) 9 to 10 septa are quite normal. In the smaller ones (0,4-0,7 mm.) only 3 to 7 septa can be observed, but 6 septa per corallite are mostly found. Specimen which resemble Th. confluens (EICHWALD) show a great variability in: corallite-diameter (0,5-1,1 mm), number of septal ridges (upp to 12), number of pores and thickening of the skelettal elements. In spite of several thin sections there hardly is any reason to distinguish these 'confluens-type' from Th. saaremica KLAAMANN. They show many transitions to each other. The systematic classification. as proposed by OEKENTORP (1970) is used in this article. On the strength of the ramose corallum of Laceripora EICHWALD, OEKENTORP (1970) established Laceriporinae OEK., 1970. Although growth forms are used as generic features, it probably is not correct to erect a new subfamily on account of such a morfologic feature. So I placed Laceripora EICHWALD in Angoporinae STASINSKA, 1967 again.

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Nederlandse Geologische Vereniging

H. Huisman. (1976). Noordelijke zwerfsteenkoralen (10) De familie Theciidae Milne Edwards - Haime, 1849. Grondboor & Hamer, 30(6), 146–165.