. Bulletin of the British Museum (Natural History), Geology. 138 LOWER CHALK TRACE FOSSILS OF S. ENGLAND of previously described specimens of T. saxonicus is the small burrow running down the centre of the lower surface of the system. In the lectotype this is very regular, but in other specimens it clearly strays from the mid-line. Geinitz (1842) interpreted this as a juvenile sponge. My own material suggests that this is another, smaller species of Thalassinoides, which sometimes follows the mid-line of the bottom of the larger burrow, but which often leaves, passing out into the surrounding
. Bulletin of the British Museum (Natural History), Geology. 138 LOWER CHALK TRACE FOSSILS OF S. ENGLAND of previously described specimens of T. saxonicus is the small burrow running down the centre of the lower surface of the system. In the lectotype this is very regular, but in other specimens it clearly strays from the mid-line. Geinitz (1842) interpreted this as a juvenile sponge. My own material suggests that this is another, smaller species of Thalassinoides, which sometimes follows the mid-line of the bottom of the larger burrow, but which often leaves, passing out into the surrounding sediment (PL 6, fig. 4). These smaller burrows may be the products of the juveniles of the T. saxonicus animal, but as I have never seen transitions it is regarded as a distinct form, T. ornatus nov. (p. 141). Whilst most systems correspond to the above description, occasionally tunnels are found filled with coarse, sandy chalk made up of shell fragments and microfossils. This material represents the remains of the burrow filling after the inhabitant has. B C Fig. 3. Alternative interpretations of laminated structures, a. As surface trace; b. As partially filled burrow; c. As totally filled burrow with semi-circular section. All xj. sifted out the finer portion for ingestion; the faecal pellets associated with these burrows show only fine-grained material when sectioned (Wilcox 1953), suggesting this mode of feeding. Presumably the coarser debris was normally removed from the system and washed away by bottom currents, being only occasionally packed into a disused part of the burrow. In a single instance, from the Upper Cenomanian at Dover, a large mass of this coarse debris, lying above a T. saxonicus system seemed to represent material dumped outside the burrow opening adjoining the entrance shaft. Thalassinoides saxonicus and " Laminated structures ". I have used the name " laminated structures" (Kennedy 1967) for problematic structures occurring throughou
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