HEMITRYPA. 179 



1. Hemitrypa ocdlata, Phillips. PI. XIX, figs. 13 — 20. 



1841. Hemitrypa oculata, Phillips. Pal. Foss., p. 27, pi. xiii, figs. 38 a — e. 



1848. — — Bronn. Handbuch, vol. i, p. 5S6. 



1849. — — d'Orbigny. Prodrome, vol. i, p. 101. 



1855. — — Sandberger. Verst. Rhein. Nassau, p. 379, pi. xxxvi, 



figs. G, 6 a. 



Description. — Zoarium sometimes rather large, irregularly infundibuliform, 

 generally steeply conical at first and then sometimes expanding in an irregular cup. 

 and composed of a framework of branches and dissepiments surrounded by an 

 external guard. Apex or point of probable attachment minute. Branches slender, 

 straight, spheroidal in section, covered on the inward or reverse side with three or 

 four coarse longitudinal striae, and divaricating rarely, i. e. about once in eight or ten 

 fenestrules. Dissepiments slight, long, straight, narrow, non-poriferous, forming 

 nearly square, angular fenestrules, which are considerably wider than the branches. 

 Cells arranged in one closely alternating zigzag row, with mouths opening on the 

 outward face of the branch, alternately on each side of its median line ; the cells 

 thus seeming to be few, and to be situated one at the base of each pillar. Pillars 

 thin, rising perpendicularly to the branches, at about the rate of three to the 

 length of a fenestrule, and about equal in height to the width of the fenestrules, 

 supporting a guard or external framework. Guard consisting of a regular network 

 of circular apertures, formed by the union of longitudinal and transverse bars. 

 " Principal bars " exactly over and parallel to the branches, and supported by the 

 pillars, and having midway between them a second series of rather smaller " secon- 

 dary longitudinal bars," which are supported by transverse bars or scalas, so that 

 the longitudinal and transverse bars are equally numerous in a given square area. 



Size. — Some of my specimens exceed 35 mm. in diameter, but none of them 

 are perfect. 



Locality.— Lummaton. Numerous specimens are in my Collection and in the 

 British and other Museums. 



Remarks. — This elegant little fossil is decidedly common, and is very easily 

 recognised. From the accompanying species of Fenestella it is distinguished at 

 once by the smallness of its reticulation, its slight branches, and its regular short 

 oblong fenestrules, as well as by its guard, which is totally unlike any other organism 

 occurring at Lummaton. The arrangement of the cells also appears to be distinc- 

 tive, as they seem to lie rather in a single alternating row than in a double row, so 

 that the cross-section of the branch generally shows a single cell with the mouth 

 opening on one side or the other, instead of two cells side by side divided by a 

 median wall. At the same time the rows are not absolutely single, as the cells do 



