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Lophophaena nadezdae Petrushevskaya, 1971

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Benson, 1966 (part.), p. 371-373; pl. 24, figs. 16-17, (not 18):

Lithomelissa cf. galeata (Ehrenberg) ? Popofsky

?Psilomelissa galeata Ehrenberg (?), Popofsky, 1909, Deutsche SŘdpolar-Exped., vol. 10, p. 304, Pl. 33, fig. 6.

Cephalis subcylindrical to globular, with small, unequal, circular to subcircular pores separated by wide intervening bars, with numerous, generally short (some as long as 36 Ám), thin, conical spines, many of which originate from the side walls of the cephalis and extend nearly vertically. Cephalis separated from a generally smooth, narrow, subcylindrical to slightly conical thorax by an indistinct collar stricture and generally a distinct change in contour of the upper part of the thorax; pores of the upper part of the thorax similar to those of the cephalis, those of its lower part subpolygonal, slightly larger, separated by thin intervening bars, and with a tendency toward arrangement in transverse rows; numerous but generally indistinct longitudinal thoracic ribs distinguishable near the mouth where they extend as short, thin, conical spines; terminal margin of thorax incomplete, mouth not constricted. Four collar pores present; cardinal pores of type B. A short, thin, conical vertical spine extends from the base of the cephalis. Apical bar a dorsal rib in the cephalis without large pores disposed on either side of it; a thin, conical apical spine extends from this rib and arises from the dorsal-cephalic face. Dorsal and primary lateral bars extend as indistinct thoracic ribs for a short distance and terminate as thin, conical, indistinct spines below the change in contour of the thorax.

Measurements; based on 30 specimens from stations 60, 71, 191, and 192: length of cephalis 23-52 Ám, of thorax 31-90 Ám; breadth of cephalis 27-37 Ám, of thorax 42-70 Ám; length of apical spine 2-28 Ám, of vertical spine 5-9 Ám, of dorsal and primary lateral spines 6-15 Ám.

Remarks. This species is distinguished from Lithomelissa thoracites and L. hystrix by the thin, conical, three-bladed, primary basal and apical spines, by the narrow subcylindrical cephalis and thorax, and by the lack of a distinct collar stricture. In a few specimens the thorax has nearly the same breadth as the cephalis.
Although Popofsky (1913) gives no description of a species he tentatively identified as Psilomelissa galeata Ehrenberg, his illustration of it is similar to the Gulf species but lacks spines originating from the cephalis. The shape of the cephalis and thorax and the nature of the pores are similar to those of the Gulf species. A few specimens from the Gulf have cephalic spines that are very short or lacking, thus conforming to the genus Psilomelissa Haeckel, but the majority of specimens have at least a nearly vertical but inconspicuous apical spine and a short vertical spine; therefore, there is no doubt that this species belongs in Lithomelissa Ehrenberg. Without reference to Popofsky's type material, identification of the Gulf forms with his species is not positive.

Distribution. This species is cosmopolitan in the Gulf, rare at all stations where present in the southern Gulf, and rare to common in the northern Gulf. It is absent at stations 90, 95, 99, 130, 194, and all those to the north. It is common at stations 191 (3.2%) and 192 (2.2%) in the northernmost diatomite region. Its greater frequency in the northern Gulf is the result of upwelling.
Popofsky (1909, p. 304) reports Psilomelissa galeata Ehrenberg (?) from the tropical part of the South Atlantic. Further taxonomic study is needed before a definite statement can be made about the distribution of the Gulf species.
Benson 1966


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