CYCLUS B1L0BATUS. 249 



eyes really covered those organs ; and further, that the ribbed border protected the feet 

 when the animal was in repose. 



We must differ from M. de Koninck in referring this form to the Trilobita. If 

 truly an adult, it must be placed near Apus with the other shield-bearing Phyllopoda. 

 If a larval form, it may have been the early stage of Prestwichia or some other, of the 

 Coal-measure Limulidce. Nor do we think it in the least probable that the shield of 

 Cyclus radialis was flexible or contractile, its original segments being completely soldered 

 together into one piece. 



If we except Cyclus Bankini (PI. XXXII, fig. 42), which may have been chitinous 

 in its substance like the modern Limulus, the other species seem to have had a firm 

 calcareous covering like the test of Phittipfda and Brachymetopu-s, found associated with 

 them in the same beds of Carboniferous Limestone in Yorkshire, Ireland, and Belgium. 



Species 1.— CYCLUS BILOBATUS :— H. Woodw., 1870. PL XXXII, fig. 45 a, b. 



Cyclus bilobatus, H. Woodw., 18/0. Geol. Mag., vol. vii, p. 554, pi. xxiii, figs. 



3, 3 a. 

 — — H. Woodw., 1873. Brit. Assoc, 7th Report on Fossil Crustacea, 



p. 304. 



This specimen is from Settle, in Yorkshire, and was collected by Mr. J. H. Burrow. 

 Its greatest length is 3 lines. Viewed in profile it is nearly hemispherical (see 

 fig. 45 b), its greatest elevation being 1^ line. In general form it reminds us 

 strongly of the dorsal aspect of certain Coleopterous Insects of the genus Coccinetta or 

 Cassida, the elytra being represented by the two large smooth posterior lobes of the 

 shield, with their dividing ridge, and the head and thorax by the anterior third. The 

 border is not flattened and curved outwards in this species, as in C. radialis and some 

 others, but is bent downwards and terminates abruptly at the same angle as the rest of 

 the carapace (see fig. 45 b). The frontal margin was probably divided into six parts, but 

 it is only imperfectly preserved. 



The anterior part of the carapace or buckler is divided transversely from the 

 posterior and larger portion by what, for convenience, we may call " the cervical 

 furrow," whilst a median or " dorsal furrow," divides it down the centre for about one 

 fourth of its entire length, thus separating the anterior parts into two equal lobes ; here 

 the median furrow diverges right and left in a crescent-shaped curve, and unites with the 

 cervical furrow, leaving a small elevated median area (cardiac region?), which contracts 

 rapidly backwards and is then prolonged as a narrow dorsal ridge — dividing the two 



