Silurian.} PALAEONTOLOGY OF VICTORIA. [Trilobites. 



length of head, 9 lines ; width, 1 inch 6 lines ; leno-th of head in lars'S perfect speci- 

 men fif<ured, lUJ lines; width, 1 inch lOlines; greatest width of glabella, ]0| lines; 

 length of eye, 4 lines ; length of pygidium, 8 lines; width, 1 inch 6 lines. 



Reference. — P. Jecundus (Barrande), Systems Sil. (la la Bohem. p. 514, t. 21, 

 fig's. 1-27. 



The Phacops fecundus of Barrande, belonging to my sub-genus 

 Portlockia, occiu's in the utmost profusion fi-om the bottom to tlie 

 top of all the stages of the Upper Silurian rocks of the basin of 

 Bohemia, not occurring at all in the Lower Silurian below, but in 

 numerous localities in the Bohemian basin suddenly ajijiearing in 

 myriads in the Upper Silurian strata as their most abundant Trilobite. 

 It is not, however, found to my knowledge in Great Britain or any 

 other part of Europe or America* where those rocks occur, so that 

 my recognition of it as one of the most abundant of the Upper 

 Silurian Trilobites of Victoria is of the highest interest in connection 

 with the distribution of species in space. 



As M. Barrande has pointed out, this Trilobite may be easily 

 distinguished from the very similar P. latifrons (Bronn) of the 

 Devonian rocks, by the eye being always considerably in advance 

 of the posterior furrow of the cheeks, and by the impressed line 

 along the middle of each of the flatter lateral ridges of the pygidium. 



Common in the Upper Silurian sandy, yellow, and red, beds 

 (probably identical with the May Hill sandstone) at Section 12, 

 parish of Yering. 



Explanation of Fioures. 



Plate XXII. — Fig. 8, cephalic shield of ordinary size and proportion showing the eyes and 

 granulation and direction of eye-line, natural size. Fig. 9, small pygidium, natural size. (The 

 duplicating furrow on lateral ridges has become too indistinct in the lithograjih.) Plate XXIII. 

 — Fig. 1, cephalic shield compressed laterally so as to be less than the normal width, natural 

 size. Fig. 2, cephalic shield of large perfect inrolled specimen slightly extended laterally, eye- 

 line indistinct, natural size. Fig. .3, perfect thorax and pygidium (the inrolled head of which is 

 represented by fig. 2) showing the large tubercular ends of the segments of the axal lobe of 

 thorax (in this figure also the faint duplicating furrow on each lateral rib of the pygidium has 

 become too indistinct in the lithographing), natural size. Fig. 4, pygidium slightly compressed 

 laterally, so as to seem narrower than the normal form, natural size. Fig. 5, pygidium slightly 

 ividened by pressure, natural size. (On figures 4 and 5 the faint dividing fuiTow of each lateral 

 ridge has too nearly disappeared in the printing.) Fig. 6, eye, mognified, showing the number 

 and arrangement of the lenses. Fig. 6a, portion of ditto more highly magnified, showing the cups 

 from which spherical lensea of each division of the compound eye have fallen out. 



* The P/iacnps Logani of Professor Hall (Pal. N. Y., v. 3, pt. 1, p. 353, t. 73, f. 15-25), from 

 the Lower Helderberg group, is supposed to be distinguished from this species by the smaller 

 eyes, with fewer lenses ; but M. Barrande gives from 4 to 9 lenses in each row, and the total 

 lenses in each eye from 64 to 136 in the Bohemian species, so it is difficult to realize the distinc- 

 tion suggested by Prof. Hall. 



[ 16 ] 



