This is the first reported occurrence of the Middle Ordovician sponge Lissocoelia sp. cf. ramosa BASSLER from Europe. Dredged up in a large water-filled sand-pit situated in the north-eastern part of the Overijssel province in Holland, the sponge was found embedded in a silicified limestone driftboulder originating in the Baltic area. Associated with Lissocoelia are three globular sponges, two of which are specimens of Hindia (Microspongia) fibrosa HINDE as could be proved by microscopical examination of the spicular network at the periphery of the sponge body. Lissocoelia ramosa is a fairly common appearance in the Antelope Valley Limestone of Central Nevada. This horizon belongs to the Whiterock stage of the Ordovician of North America (lowest Chazyan) and has its equivalence in the European Llanvirn. Finds of Lissocoelia of the same age are also known from the Mazourka Canyon area in California (9. 1963, p. 568, 569, p l. 63, fig. 8, 9). As the late Dr. P. Kruizinga, a well-known Netherlands geologist, stated (personal communication), this particular limestone driftboulder is of Caradocian age (1. 1918. p. 89-92; 2. 1967, p. 51, 58). This implies that the genus Lissocoelia ranges from the lowermost Chazyan into the Caradocian and that also the associated Hindia specimens are of the same age as the North American specimens (earliest occurrences there being Porterfield, or Caradocian). The Lissocoelia from Overijssel differs from the American types in having a single cylindrical body whereas the latter are recognized by their dichotomously branched stems (3. 1941, p. 96, pl. 19, fig. 9; 9. 1963, p. 568, 569, p1. 63, fig. 9). Unusual are the short root-like protrusions appearing only at one side of the body. The spicular network is built up by dendroclones which arc arranged in ladder-like, vertically running series diverging to the periphery of the sponge body. The spicules, measuring from 0.21 to ca. 0.37 mm, seem to have slightly larger dimensions than those of the Nevada specimens which are about 0.20 mm in length (3. 1941, pl. 19, fig. 11; pl. 24, fig. 5). In view of the above mentioned remarkable differences it is possible that the Lissocoelia from Overijssel represents a new species. However, on the other hand we have to take into account that these deviations may be only individual adaptations to certain ecological conditions.

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Th.M.G. van Kempen. (1969). Lissocoelia sp. cf. ramosa BASSLER in een verkiezelde kalksteen als zwerfsteen uit Twente, provincie Overijssel. Grondboor & Hamer, 23(3), 101–108.