The monophyly of the genus Echinocardium is based on two synapomorphies: an anal branch is added to the subanal fasciole, and the labrum is short and bordered by two pairs of ambulacral plates.
Subanal fasciole. Synapomorphy: anal branch present.
Relative size of the internal fasciole. Synapomorphy: the length of the internal fasciole reaches 50% of the test length [ILLUSTRATION FOR FIGURES 1-3 OMITTED].
Number of pore pairs of the frontal ambulacrum enclosed in the internal fasciole. Synapomorphy: many more than ten pore pairs enclosed in the fasciole [ILLUSTRATION FOR FIGURE 1 OMITTED].
Spiral ridges thinner than axials in intervals, expanding on ribs to form angular nodules, ridges nearly equal in strength, adapical row slightly the stronger, abapical one slightly weaker; first two whorls with two rows of nodules plus a third usually beginning to develop above suture, later whorls with three main rows of nodules, plus a weak ridge immediately below suture; last whorl with a shallow waist-like furrow at base of rostrum containing a thin ridge, strengthening and bearing angular nodules on dorsum; rostrum forming a moderate fasciole, which bears 3 ridges weakening anteriorly, the upper 2 with angular nodules.
Description: Shell fusiform with truncated base; b/l 0.35-0.38, a/l 0.38-0.41; whorls strongly convex with narrow angular shoulder, and undulant, fairly deep suture, base of last whorl without a waist-like constriction; rostrum narrow, without a fasciole; aperture narrowly elliptical; siphonal canal strongly contracted but slightly expanded terminally, end truncate, oblique in dorsal view, not notched.
Description: Shell fusiform with high, orthoconoid spire and truncated base; b/l 0.380.43, a/l 0.33-0.39; whorls convex, not shouldered, subsutural region concave and sloping, suture not undulating, base of last whorl constricted above rostrum into a deeply concave "waist"; rostrum forming a strongly convex fasciole; aperture narrowly elliptical; siphonal canal strongly contracted but expanded terminally, end truncate, in dorsal view concave, with a slight projection medially.
Axial ribs straight, slightly prosocline, moderately weak below suture, evanescing below "waist", fasciole with strong nodules; ribs in t/s more or less angularly rounded, with sloping sides, ribs wider than their intervals, 8 per whorl; bases of ribs narrowing where they cross basal "waist", where they are separated by foveolate interstices.