Ilydractiuia, Parkeria, a/tJ Stroniatopora. 71 



tonora striatella obtained from the Silurian tbrniation at 

 Wenlock. It is coniposed ot" yellowish-grey eonipact linie- 

 Htone, cylindrical in turni, obtusely conical at the IVee end, and 

 truncated at the lixed one, Avhich is fractured, about /3 inches 

 long and 1^ inch in diameter; granulated on the surface and 

 covered more or less with papilliform eminences, each of which 

 (about l-20th inch in diameter) appears to have had an ojjcning 

 in the sunnnit, about 8-18U0ths inch in diameter, now filled up 

 with calcspar (Hg. 24, ^), in the midst of which are stellated 

 (fig. 24, a) with centres respectively about -^- of an inch apart, and 

 composed of radiating branched grooves in the surface, whose 

 ultimate divisions meet those of the neighbouring stellates; each 

 stellate also appears to have had a papilliform eminence in the 

 centre, about 24-1 sooths inch, with tlie appearance of an aperture 

 in its summit about 8-1800tlis inch in diameter, now also tilled 

 with calcspar ; while i\\Q,fond ox granulated surface is produced, 

 as before stated, by the weathering out of the interstices of a 

 reticulated tissue-fibre like that of Parkeria, &c. Internally, 

 on the other hand, the structure is lamiuated and concentric, 

 irregularly undulating in accordance with the irregularities on 

 the surface during the successive periods of growth. It is not 

 difficult to see that the tubular spaces, which communicate 

 with each other in the midst of the reticulated tissue-fibre, 

 finally terminated on the surface; and on examining the 

 ce7itre of the fossil, Mr. Sollas and myself observed a foreign 

 body bearing very much the appearance of a fragment of an 

 Orthoceras (fig. 25, «) , which is at least ~ of an inch long and 

 I of an inch in diameter, filled wath transparent calcspar, whose 

 homogeneity contrasts strongly with the tortuous tissue-fibre 

 of the Stromatopora generally, and presenting three distinct 

 septa towards the largest end, with a fourth, which probably, 

 from its appearance, teiiuinatcs this part ; while the shell-sub- 

 stance on the sides presents under the microscope an obliquely 

 laminated structure throughout, indicative of its having been 

 formed of the consecutive concave layers of the septa 

 generally. 



Obs. Now lierc we have a very similar stiiieture to Parkcn'a, 

 with a concamcrated shell for a foreign body in the centre, 

 while the surface is somewhat like that of Lojinsia, with the 

 stellates more evidently developed as in Stromatojwra, all in a 

 fossil so far back as the Upper Silurian System. 



After this, Mr. Sollas showed me a fragment of a specimen 

 of a calcareous Stromatopora from the Devonian Limestone, 

 of which a polished section had been inade vertically to the 

 lamination, and therefore longitudinally with the tubulation. 

 Here the base or tissue, if it may be so called, is not fibrous 



