THE FAUNA OF THK ST. JOHN GROUP. S3 



verse septa, and the straight part is doubled on the ventral side by a delicate partitioTi 

 connected with the ventral side by very thin somewhat distant septa or diaphragms. The 

 dorsal side terminates at the aperture in an elliptical lip, and appears to be smooth, except 

 near the aperture and apex, where a few distant, faint stria? are found. The ventral side 

 is rounded, but is not well exhibited in the examples known. 



The operciilum of the type of this species is not known. 



The internal structure of this shell is shown by an example in a dark phosphatic 

 nodule from the sandstones of 1.^*1 In this the inside of the body cavity is filled with a 

 grey deposit of a lighter color than the mass of the nodule ; a narrow band along the side, 

 wall of the cavity is filled with a deposit of still lighter color, which may be seen to be 

 separated from the deposit in the body cavity by a faint dark line, marking the place of 

 the inner partition of the shell ; there are also faint transverse lines at intervals along this 

 band, which are fragments of transverse diaphragms. The septa in the lower or camerated 

 portion of the tube, below the body cavity, are thicker than those at the side of it, and go 

 entirely across the shell. 



CyrMheca haimila, Hicks, of the British Menevian fauna, may be congeneric with this 

 shell. It possesses a similar cui-ved apex. 



Length, Y mm. Width, 1 J mm. Rate of tapering, 1 to 5. 



Locality and Horizon. Infrequent in l.b^ at Hanford Brook, St. Martin's, and this or a 

 similar species is occasionally found in l.c^ at the same locality. 



DiPLOTHECA Hyattiana, vur. a. CAUDATA, n. var. (Plate VI. Figs, ô and -ya.) 



This is a very marked variety, and may be a distinct species. Form that of an elon- 

 gated cone, which, as preserved in the shales, is flattened on the dorsal side. The shell 

 tapers uniformly to the apex, which is subulate ; in numerous examjjles the point is 

 attenuated into a flexible cauda or tubule crossed at intervals by raised annulations. The 

 doi'sal side of this variety is thin and smooth, and terminates in a semi-circular lip at the 

 aperture. The ventral side is more strongly arched, and has a raised central band which 

 . is preserved in the shale as a smooth rounded rib, about one third of the width of this 

 face of the shell. 



The operculum is a^)o^^t as wide as long, and has an elevated marginal ridge, low and 

 rounded, extending around the dorsal and lateral sides. The ventral slope is convex, and 

 has two sharply-cut grooves on each side, radiating toward the margin. The lateral slopes 

 are depressed, strongly defined at the front and outer margins, and have several faint, 

 slightly-arched radiating stria^. The dorsal slope is convex, raised aboA-e the rest of the 

 operculum, and has concave side margins, the surface is smooth, or with a faint median 

 line. The cast apparently of this operculum has a pair of grooves, wide and deep at their 

 their extremities, extending on each side of the nucleus, along the back of the lateral slope 

 until they meet the projecting extremities of the marginal ridge. 



Sculpture. The shell of this variety has a shining surface, especially when viewed 

 lengthwise ; a lens of high power resolves the very fine striae which cross the shell trans- 

 versely, arching up over the dorsal face ; the ridges due to periodical cessation of growth, 

 seen on other species, are not visible on this variety. There are two or three straight 

 longitudinal strim, nearly parallel to the sides of the shell, visible on each side of the veu- 



