474 Messrs. W. K. Parker and T. R. Jones on the 



Foraminifers presenting the aspect of a little half-ring, formed 

 of four or more thick -walled^ hollow, subquadrangular segments, 

 arranged side by side seraicircularly, each chamber opening by 

 a nipple-shaped aperture on the concave surface of the half-ring, 

 and communicating with its neighbour by a rather large sub- 

 central aperture in the septal face. The shell-structure resem- 

 bles that of the "opake" Foraminifers. The surface of this 

 semi- annular shell is nearly smooth and rather polished, and is 

 sulcated at the junctions of the chambers. Rarely is the half- 

 ring truly semicircular, the segments being often arranged on a 

 gently curved line, and ofiFering a resemblance to a slightly bent 

 larva or caterpillar. Such a form as this (which we term Dac- 

 tylopora eruca) is also found in some of the French Tertiaries ; 

 and here, besides this pupoid form, a still greater departure 

 from the ring-shape is made sometimes by the cells becoming- 

 short cylinders perforated at both ends, partially separated one 

 from another, and something like fragments of Tubulipora or 

 CellijJora. This is our variety D. di(jitata. 



c &, d. Varieties D. annulus and D. marginoporella. In the 

 Calcaire grossier of Grignon and other Tertiary deposits we find 

 these demi-rings, and also numerous little perfect rings, having 

 the same structure as the less perfect half-ringed shells. Of 

 these annular forms, some present neatly packed chambers, and 

 others divaricating subtubulai- chambers. A specimen of the 

 latter has been figured and described by Michelin (Icon. Zooph. 

 p. 177, pi. 46. f. 27) under the name of Clypeina marginoporella. 

 The former variety we name D. annulus. 



e. Var. D. reticulata. Besides these, there are in the Calcaire 

 grossier of France, and in the Miocene beds of San Domingo, 

 compound forms, made up of two or many such rings, mounted 

 one on another symmetrically, each junction being marked by a 

 regular series of minute round holes left by the apposition of 

 the septal sulci of the two rings. The shell-substance between 

 the cells is thick; but the outer wall of the chambers, being 

 thinner, is frequently worn away, so that the specimens present 

 large pits or openings beside the junctural interspaces. This 

 variety is the Larvaria reticulata of Defrance, Diet. Sc. Nat. 

 XXV. p. 287. 



/. Var. D. perforata. There is a variety of Dactylopora, in the 

 Grignon shell-sand, which much resembles D. reticulata ; but 

 the cells open outwards as well as inwards. Hence we term it 

 D. perforata. The apertures, both external and internal, are 

 large and lipped ; the former are in the centre of the thin outer 

 cell-wall, and present superficially nearly regular circles of pus- 

 tulous openings. The interseptal spaces are, as a rule, hidden 

 in this form. 



