W. B. R. King — Notes on the Genus Sp]tcerocory2:>Jie. 583 



rise sharply from tlie groove which separates it from the central 

 raised portion. At the lateral extremity of the frontal ridge the 

 groove reaches the margin of the hypostome, thus forming a break 

 in the raised marginal ring. This also makes two notches in the 

 general square outline. The lateral margins are raised and thickened, 

 particularly just below the notch mentioned, above and at the 

 posterior angles. The angle between the lateral and posterior 

 parts of the margin is sharp and about 90 degrees. The central 

 part of the posterior border is bent slightly towards the centre of 

 the hyjiostome. There are indications of a small pit in the groove 

 opposite the posterior edge of the notch in the position shown in 

 the restoration. The surface of the hypostome is finely granulated, 

 as shown by its " cast ". 



From the restoration it will be seen that the hypostome is similar 

 in type to the typical Cheirurid hypostome, such as that of Clieirurus 

 himucronatus Murch.^ or Barrande's figures of Cheirurid hypostomes 

 in his Systeme Silurien,^ but the hypostome which shows more points 

 in common than any other is that of Deiphon forhesii Barr.^ In 

 Devphon there is the same central spherical raised portion separated 

 by the marked groove from the raised marginal ring. The general 

 outline is almost exactly the same in each case. In DeipTion the 

 granulations on the central ]3ortion are more marked {vide Salter's 

 figure) than in SphcBrocoryphe, but this may well be a result of the 

 development of one from the other. Dr. Cowper Reed ■* has shown 

 that the various characteristics of Deiphon appear to be developed 

 from the rather less specialized form which is found in Sphcerocoryphe 

 and the discovery of the hypostome, which has been shoAvn to be of 

 great use in deciding family relationships, certainly bears out his 

 views. 



Turming now to the hypostome of Staurocephalus, an examination 

 of the specimen in the British Museum figured by Salter ^ shows 

 several points which are not brought out very clearly in the figure. 

 Firstly the specimen has suffered considerably during the develop- 

 ment to which it has been subjected. The result is that the posterior 

 part has been broken away to a great extent. The two knobs 

 about the centre of the hypostome are clearly shown in the figure, 

 but on the right-hand side, looking at the hypostome, there is clear 

 evidence that once the anterior part of the hy])ostome extended 

 laterally in the form of a wing. Just behind this wing there is a 

 slight ledge, which may be a fragment of a border on a lower level. 

 If this really be the case then the hypostome of Staurocefhalus 

 would consist of a flattish margin with marked wings and a sharply 



^ Salter, " British Trilobites " : Palseont. Soc, pi. vi, fig. 11. 



2 Barrande, SyMeiiie Silurien, vol. i, pis. xli-xlii. 



» Salter, "British Trilobites": Palsoont. Soc, pi vii, fig. 10; and 

 Lindstrom, " Forteckning pa Gotlands Siluriska Crustaceer opersigt. af 

 k. Vetenskaps-Akadeniens Forhandlinger," 1885, No. 6, p. 37, and pi. xv, fig. 18. 



* F. R. C. Reed, Geol. Mag., 1898, p. 211. 



^ Salter, op. cit., pi. vii, fig. 17. 



