Vaquerosella andersoni (Twitchell, 1915)

Martínez-Melo, Alejandra & Alvarado-Ortega, Jesús, 2020, Vaquerosella perrillatae sp. nov.: A Miocene species of Echinarachniidae (Echinodermata: Clypeasteroida) from Baja California Sur, Mexico, Palaeontologia Electronica (a 14) 23 (1), pp. 1-18 : 6-8

Vaquerosella andersoni (Twitchell, 1915)

Scutella andersoni Twitchell in Clark and Twitchell, 1915. Kew, 1920. Loel and Corey, 1932.

Echinarachnius andersoni Twitchell. Grant and Hertlein, 1938 .

Vaquerosella andersoni . Adegoke, 1969.

Description (Twitchell, 1915). The test is small, ranging from less than one-half to slightly more than an inch in diameter. In marginal outline it is suboval to broadly subovate; broadest posteriorly, usually about as long as wide. The margin is thin, more so posteriorly than anteriorly, with rather pronounced notches opposite the posterior petals and sometimes with faintly defined notches opposite the anterior paired petals. The whole form is greatly depressed; the upper surface having a more or less well defined ridge extending along the longitudinal median line and involving the odd petal, the inner ends of the other petals, and the inner portion of the posterior interambulacrum; from the median ridge the surface slopes at first steeply then gradually away to the side edges. The under surface is slightly concave longitudinally. The apex is excentric anteriorly, at the highest point of the median ridge.

The ambulacral areas are rather narrow; the dorsal portions petaloid. The petals are moderate size, subelliptical, extending more than halfway to the margin, open at the ends, the odd petal more widely open than the others. The poriferous zones are relatively wide, though slightly less so than the interporiferous areas; pores oval, pairs of pores conjugated. The interambulacral areas are rather broad with the exception of the odd posterior area, which is narrow. The surface of the test is covered with small uniform tubercles. The apical system is decidedly excentric anteriorly, about coincident with the apex. There is a large, subcircular madreporite, four large genital pores, of which the anterior pair are somewhat nearer together than the posterior pair, and five small radial plates each perforated by a minute pore. The peristome is excentric anteriorly. The character of the ambulacral furrows cannot be made out on the specimens studied. The periproct is very small, circular, and supramarginal, almost marginal.