From Fensome et al., 2019:
Beyrichodinium hystrix Below, 1990, p.70–71, pl.17, figs.1–5. Holotype: Below, 1990, pl.17, figs.1–5. Contrary to the opinion of
Lentin and Williams (1993, p.61), we consider this name to be validly published. Below (1987a, p.6) stated that, unless otherwise indicated, all the material is in his personal collection. Since Below (1987a, 1987b, 1990) are parts I to III of a single study, we agree with J. Jansonius (personal communication) that Below's (1987a) repository statement refers to all three publications, fulfilling the requirement of ICN Article 40.7 (see also the discussion on Article 40.7 in the Introduction). Age: early Hauterivian.

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Original description (Below, 1990) (translated from German):

Beyrichodinium hystrix n. gen. n. sp.
Plate 17, Figs. 1-5

Derivatio nominis: Named after the Greek word for spiny.
Holotype: Specimen S1-1505(K2)2/15 (Plate 17, Figs. 1-5).
Locus typicus: Moorberg brickworks, Sarstedt.
Stratum typicum: Subcutaneous, amblygonium zone.

Description:
Vesicle/plate arrangement of the dinoflagellate Amphiesma cop, pop, cap, 3', 3a, 6'', 7c, 6'", 2"", as, FM, ls, rs, ps; tegulation ?4*, ?3**, ?4***, 2****, 7c, ?4 . , ?4 .. , ?3 ... ; growth of thecal plates in a ?gonyaulocoid manner;
Zygote cyst habitus proximochorate, acavate, also apiculocavate, spheroidal; wall composed of a thin pedium and tough, granular, prismatic luxuria, surface chagrinate and with numerous, short, abruptly attached, slender, cylindrical, solid or hollow but distally closed evexate processes 1/3 to 1/4 the central body diameter in length occupied, number of processes varies individually, arrangement irregular, in finate, penile and intra-areater position; accedation scheme NR PR/X PR, NR', 1a(arch), 2a(arch), 3a(arch),, NR'', NRc, NR'", NR'"', NRs; PR occasionally as a low bulge; 3 anterior intercalaries as opercular plates separated by archaeopyle sutures, camerate la (L), fastigiate 2a (D) and caroidale 3a (R); anterior bigeniculate 1'' (VVL), anterior lineare 2" (L), anterior geniculate 3" (DDL), anterior geniculate 4'' (DR), with potential finis 3" /4'" dorsal, anterior geniculate 5'' (RVR); archaeopyle anterior intercalary 1a + 2a + 3a; operculum solvate, Opercular plates secat, general opercular formula 1a(s), + 2a(s) + 3a(s).

Dimensions of the holotype:
Length 40 μm, width 40 μm, thickness 40 μm.

Reference:
Specimen 1505.