10.--Crisia (?) Johnstoniana. (G. A. M.) × 250 linear. _S. s. Maidstone._ 10_b_.--Two cells of the coral, _fig._ 10, seen in profile, × ×. 11.--Homœsolen ramulosus; _nat._ _Cret. Lewes._ 12.--Idmonea Dixoniana; a portion of _fig._ 6. ×. 13.--Retepora laxa. _Mt. L. Ph. Yorks._ 13†.--A portion of the same ×. 14.--Idmonea Comptoniana. × ×. (G. A. M.) _Chalk, Chichester._ (_Mr. Walter Mantell._) The small figure on the right is of the natural size. ] [Sidenote: MICROSCOPIC FOSSIL BRYOZOA.] Crisia Johnstoniana. _Lign. 89, fig. 3, 10, 10b._--The minute recent corals thus designated are allied to _Flustra_, but separated from that genus by the cells being disposed in a single series, and united by connecting tubes. I notice this genus to direct attention to a very curious polypidom from the Greensand of Maidstone, presented to me by Mr. Bensted. The specimen is attached to a fragment of shell. The cells, five of which are represented, _fig._ 10, are elliptical, with the aperture above, and towards one extremity; they are united by very slender, hollow filaments: _fig. 3_, two of the cells seen from above × 250 linear; _fig. 10b_ the same seen in profile.[253] I have named this species _C. Johnstoniana_, as a tribute of respect to the author of the admirable works on British Zoophytes, previously noticed. [253] I refer this fossil to the genus _Crisia_ with some hesitation; perhaps _Hippathoea_ would be more correct, but all the described species of the latter are branched. The fragmentary relics of numerous minute and elegant corals, constitute a considerable portion of the mass of some of the white chalk strata; several genera of these zoophytes are figured in Mr. Dixon's beautiful work, and described by Mr. Lonsdale. Attached to the surface of shells, &c., and sometimes standing erect in little crannies, or hollows, of the flints, many beautiful corals may often be detected with the aid of a lens. By brushing chalk in cold water, and examining the deposit, the student will probably discover several of the species figured in _Lign. 89_, which we proceed to describe. Retepora (_Lace-Coral_). _Lign. 89, fig. 13._--A very thin calcareous polyparium, disposed like net-work in foliaceous and branching plates; cells opening either on the upper or inner side. These are an elegant tribe of corals, of which many species occur in the Chalk formation at Maestricht, in the white-chalk of England, in the mountain limestone of Yorkshire, (_Phil. York._), and in the Silurian deposits (_Sil. Syst._). It may be useful to state, that in the description of the fossil retepores, the openings in the net-work are called fenestrules--the spaces between the ends, _dissepiments_--and those between the fenestrules, interstices. A delicate fossil retepore from the mountain limestone of Yorkshire (_R. flexa_), is figured _Lign. 89, fig. 13_.