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Lophocyrtis leptetrum (Sanfilippo and Riedel, 1970)

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Cyclampterium ? leptetrum Sanfilippo and Riedel. n. sp.
Plate 2. figures 11-12

Description: Shell generally robust, campanulate to subspherical. Cephalis subspherical, usually poreless but occasionally with a f ew small pores; thick-walled, especially at the apex. Collar stricture pronounced. Thorax hemispherical or slightly inflated, thick-walled, with subregular circular pores, and a surface which is nodose or, less commonly, only slightly rough or thorny. Abdomen commonly inverted cap-shaped, closed distally. but in some specimens open subcylindrical.
Abdominal pores irregular in size and arrange ment, generally as large to twice as large as the thoracic pores, generally smaller and more regular than the abdominal pores of C. ?pegetrum. Three to five irregular, subcylindrical. terminal or subterminal feet are present in rare specimens.

Measurements: Based on 30 specimens from cores AMPH 91P, 558-561 cm.; JYN V 20P. 214-216 cm .; MSN 135P, 174-176 cm . ; SDSE 91, 319-320 cm. and 820-821 cm.; WAH 7P , 257-259 cm. and 519-521 cm. Total length 225-440 Ám. Length of thorax 150-165 Ám (rarely to 180 Ám), its maximum breadth 195-250 Ám.

Remarks: This species is distinguished from C. ? pegetrum by the larger dimensions of the thorax, and the generally smaller, less irregular pores of the abdomen. It is distinguished from C. ? tanythorax by Ihe less inflated form and commonly nodose surface of the thorax, and by the more irregular abdominal pores. The specific name is derived from the Greek leptos=thin, and etron=abdomen.
Sanfilippo and Riedel 1970
Lophocyrtis (Cyclampterium) leptetrum (Plate II, 6 9)

Remarks: Lophocyrtis ( Cyclampterium ) leptetrum shows a lot of variation in the nature of the thoracic wall and the shape and size of the abdomen. No consistent combination of these two characters with time has yet been found. The hemispherical to inflated thorax can be thickwalled and tuberose (Plate II, 7-9), to thinner walled with a rough or thorny surface. The abdomen may be cylindrical (Plate II, 8 ) or inverted cap-shaped, of varying length (Plate II, 6, 7 ) and with or without feet.

L. (C.) leptetrum is distinguished from its ancestor, L. (C.) pegetrum, by the larger dimensions of the thorax, especially its length and by the abdominal pores generally being smaller. From its descendant L. (C.) tanythorax it differs by its shorter thorax.

New observations (on 25 specimens from DSDP Site 77B Core 29; Site 289 Cores 45, 46, 54, 59, 62, 64; Site 398D Cores 8, 9 and Site 515B Cores 13, 22 ):
total lenth 225-440 Ám; length of thorax 150-180 Ám, width 170-270 Ám, number of pores around the circumference 28-34; length of abdomen 65-220 Ám, width 135-310 Ám, number of pores around the circumference 12-27. No horn.

L. { C.) leptetrum occurs in moderate abundance in the Early Miocene, from its evolutionary origin in the middle of the Cyrtocapsella tetrapera Zone to its transition to L. (C.) tanythorax in the middle of the Calocycletta costata Zone.
Sanfilippo 1990











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