168 Dr. Ivor Thomas, — Nofe on PhacopH Icevis. 



much more accentuated in the former than in the latter. The 

 question is still further complicated by the fact that Giimbel 

 (4, p. 495, pi. A, figs. 7-9) refigures what he expressly states is the 

 original of T. ? lavis, Miinst. His figure shows the presence of 

 well-marked eyes, together with granules over the surface of the 

 head-shield. Other differences are easily recognizable on comparison 

 of the two figures. Giimbel identifies the form with Ph. cryptopli- 

 thalmus, Emmr. (2, pp. 27, 40, 61), which name he retains in 

 preference to Icevis, at the same time deprecating Salter's retention 

 of the latter name. Salter, however, had expressed an opinion in 

 two of his works (13, p. 16 ; 14, p. 1) that it might be found necessary 

 to give the British form another specific name. In the later work 

 (14, p. 1) he even suggests the use, should occasion arise, of trinucleus 

 as a substitute for la;vis. 



As no traces of eyes have been noticed on any of the numerous 

 specimens of the so-called Ph. {Trimerocephalus) Icevis found in this 

 country, there is strong reason to believe that eyes were never present. 

 In this character the species would be more allied to Ph. (Tritn.) 

 anophthalmus, Freeh (3, p. 270), and Phacops ccecus, Giirich (5, p. 362, 

 pi. XV, fig. 4), in which ej^es are likewise absent, than to Ph. cryptoph- 

 thalmus, Emmr. Compared with Ph. {Trim.) anophthalmus, Freeh, 

 the angle made by the dorsal furrows bounding the glabella of the 

 Eritish form is considerably larger, the marginal border is narrower, 

 the ratio of the length of the glabella to its width is much less, 

 while the frontal margin of the glabella is more curved. 



Compared with Ph. ccscus, Giirich, the head region of the British 

 form is considerably wider in proportion to the length, and the 

 frontal margin of the glabella is less acute. The glabella and 

 cheeks of the Polish specimens are covered with granules, while 

 various other differences of detail also help to distinguish the two 

 forms. Other examples of Trimerocephalus without eyes have been 

 described by various authors, but none appears to agree with the 

 British species. 



If satisfactory traces of eyes could be found in the numerous 

 specimens from Cornwall and Devon, the form might probably be 

 allocated near to Ph. {Trim.) cryptophthalmus, Emmr., as interpreted 

 by Giimbel's figure, which is unfortunately unaccompanied by a 

 description. Ph. {Trim..) cryptophthalmus, however, furnishes another 

 instance of a confusion arising through different interpretations by 

 different authors. Thus Ph. cryptophthalmus, Eichter (9, p. 20, 

 figs. 23-31), belongs, according to a later work of the same author 

 ( 1 0, p. 11 6), to Ph. granulatus (Miinst.), while a new Ph. cryptophthalmus 

 of the same work (10, pi. ii, figs. 1-5) probably belongs to Ph. brevis- 

 simiis, Drevermann (1, p. 115, pi. xiii, fig. 3). Ph. cryptophthalmus., 

 F. Roemer (12, pi. xiii, figs. 6, 7), and PA. cryptophtlmJmus, Tietze 

 (17, pi. xxi, fig. 1), have been described by Professor Freeh as 

 Ph. {Trim.) anophthalmias. Ph. cryptophthalmus, F. Eoemer (11, 

 pi. XXXV, fig. 18), and possibly that of Sandberger (15, pi. i, fig. 6ff), 

 appear to belong to Freeh's species. The remaining figures of 

 Sandberger's cryptophthalmus represent different species. Salter's 

 Ph. cryptophthalmus (13, p. 17, pi. i, fig. 8 ; 14, pi. ix, fig. 6), which 



