. Bulletin of the British Museum (Natural History), Geology. SMITH, PAUL, GALE & DONOVAN b C. Fig. 29 Camera lucida drawings of apical discs of Glyptocyphus difficilis from the 'Upper Green- sand' of Warminster, a, ; b, ; c, there is a distinct posterior interradial notch. The anterior-posterior axis measures 40-54% of the test diameter (mean = 45%; SD = 3-5; N = 14). The minor axis measures approx- imately 90% of the major axis. The plates of the apical system are preserved in three specimens from the Upper Greensand of Warminster ( and ) (Fig. 29).
. Bulletin of the British Museum (Natural History), Geology. SMITH, PAUL, GALE & DONOVAN b C. Fig. 29 Camera lucida drawings of apical discs of Glyptocyphus difficilis from the 'Upper Green- sand' of Warminster, a, ; b, ; c, there is a distinct posterior interradial notch. The anterior-posterior axis measures 40-54% of the test diameter (mean = 45%; SD = 3-5; N = 14). The minor axis measures approx- imately 90% of the major axis. The plates of the apical system are preserved in three specimens from the Upper Greensand of Warminster ( and ) (Fig. 29). Oculars II, III and IV are exert and are small, roughly v-shaped plates. Oculars I and V are larger and are insert, separating genital 5 from genitals 1 and 4. These posterior oculars are more elongate and are rather rectangular in outline. Ocular I borders onto the periproct but ocular V may be separated from the periproct by a thin suranal plate. Genital plates 1-4 are large and abut one another. They are polygonal, each with a gonopore near the interradial margin. The madre- porite (genital plate 3) is only slightly larger than the other genital plates and the madreporic perforations are small and inconspicuous and are scattered over most of the plate surface. The posterior genital plate is small and U-shaped with a circular gonopore at its interradial point. There are, in addition, one to three suranal plates firmly incorporated into the apical disc, reducing the periproctal opening to a small oval hole lying posterior to the mid-point (Fig. 29). A large suranal plate lies anterior to the periproct, except in where there appear to be two plates. An additional wedge-shaped plate may also be present separating genital 4 and ocular V from the periproct. The periproct is thus bordered by the anterior suranal plate(s), genital plate 1, ocular I, genital 5 and the latero-posterior suranal plate. AMBULACRA. Ambulacral zones are relatively narrow, and in breadth measure 18-
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