Yol. 52.] 'ANNIVERSARY ADDRESS OF THE PRESIDENT. ciil 



the family Eryontidae, referred to the genera Polyclieles, Pentacheles, 

 Stereomastis, and Willemoesia, from the Mediterranean, the Atlantic, 

 and the Pacific, obtained from depths varying between 220 and 1900 

 fathoms. The recent species bear a very close resemblance to their 

 Liassic and Oolitic ancestors, and they offer a striking illustration 

 of the vast length of time over which a family may extend with 

 very little alteration as regards general form. 



What is the reason for the remarkable fact that so many old- 

 world genera, belonging to such varied forms as Nautilus, Pleuro- 

 tomaria, Pholadomya, Area, Caheria, Pentacrinus, Polyclieles, etc., 

 dating from the Mesozoic period rather than the modern one, 

 should still be found living in the deeper waters of our present 

 oceans ? Are we justified in concluding that they have so survived 

 because those areas have remained undisturbed since the close of 

 the Permian epoch ? Or have they been compelled to occupy the 

 deeper waters by other and stronger forms of marine life ? 



The Scillaridea might, at first sight, appear to offer an analogy, 

 in their broadly-expanded and nattened-out cephalothorax and 

 abdomen, to the genus Eryon, but they are in reality very widely 

 separated from that family (which are Astacidea), the broad and 

 serrated front of the carapace in Scyllarus, Thenus, and Ibacus 

 being largely due to the very singular modification of the great 

 pair of outer antennse, the joints of which are flattened out into 

 enormously broad and spinous fan-shaped scales, the eyes being 

 usually inserted in deep hollows near their bases at the outer 

 anterior angles of the head, but in Ibacus they are set nearer the 

 front centre. 



These singular forms are recorded as far back as the Gault, two 

 species having been noticed by me from that formation and named 

 Scyllaridia Gardneri and Scyllaridia punctata (Geol. Mag. 1873). 

 Ibacus precursor of Dames is from the Chalk Eock of the Lebanon* 

 Other species from the London Clay have been figured and described 

 as Scyllaridia Koenigii, S. Bellii, and Thenops scyllariformis, all from 

 the Isle of Sheppey. 



It is interesting to record that the late Prof, von Seebach 

 discovered and described a larval Palinurid from the Lithographic 

 stone of Solenhofen, well known — among living Crustacea — as * the 

 Glass-crab,' Phyllosoma 1 ; some of these Phyllosomce have been 

 proved to be the larval stages of the Scyllaridse. 



1 Miinster, ' Beitrage zur Petrefaktenkunde,' Heft i. p. 84, pi. viii. figs. 3, 4. 

 4to. 1839. 



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