this was published in
Martius, Carl Friedrich Phillip (1890) Flora Brasiliensis 4 (2) 201 & fig. 40.
(reprinted 1967 by Verlag von J. Kramer)
It could well be that Britton & Rose are correct when they concluded the entire description was for another plant (Cephalocereus arrabidae).
7. Cereus Macrogonus Salm-Dyck:
caule erecto columnari apice attenuato rotundato, costis plerumque 7 rarius 8-9 crassis sectione transversa semiellipticis lateribus convexis obtusis, sinubus acutis;
areolis orbicularibus vel ellipticis mediocriter distantibus tomentosis apice hand lanuginosis, aculeis periphericus pluribus validus acutissimis, centrali solitario crasso, sursum patente armatis;
[I am perhaps butchering the Latin badly but would take this last portion above to mean:
"hairy moderately-sized circular or oval areoles not distantly separated apex not wooly, finely pointed radial spines often robust, one thick central, upwards spreading spines." No mention of spine color as far as I can tell.]
floribus lateralibus solitariis crassis e media areola vel parte superiore erumpentibus basi tomento desissimo suffultis infundibuliformibus, a caule patentibus basi haud curvatis;
ovario semigloboso, cavitate latissima ovulis fasciculatim conjunctis impleta superne nuda, phyllis minutissimis carnosis triangularibus acutis vel obtusiusculis obsesso;
tubo crasse carnoso pro rata brevi superne subangustato intus profunde sulcato [p. 202:] epapilloso;
phyllis mediis abbreviatis ovato-triangularibus, majoribus stricte ovatis obtusiusculis margine extenuatis, petaloideis oblongis utrinque paulo attenuatis apice acutiusculis quam in aliis speciebus crassioribus;
staminibus tubo superiori affixis inaequilongis sed perigonio brevioribus filamentis filiformibus, antheris lineari-oblongis papillosis;
bacca depressa ambitu orbiculari praesertim superne sulcata basi rotundata perigonio marcescente coronata squamis paucis munita;
exocarpio crasso;
seminibus regulariter seriatim foveolatis subobovatis basi oblique truncatis.
Tabula nostra XI. (habitus et analysis)
Cereus macrogonus Salm-Dyck, Cact. hort. Dyck. 46 et 203; Labour. Monogr. 352; Först.-Rümpl. Handb. 706.
?Cereus hexagonus Vell. Fl. Flum. V. t. 18, text. ed. Netto, 194.
Caulis c. 7 cm. diametro subglaucescenti-viridis supra areolas non raro linea impressa transversa notatus;
costae 2-2,5 cm altae tricate inferiore vel ad medium 1,5-2 cm latae, basi ad 1,3-1,5 cm augustatae;
Areolae 1-1,5 cm inter se remotae 5-6 mm diametro tomento brevi probabiliter grieo obtectae;
Aculei periperici 3-15 mm longi teretes basi hand incrassati nigro juvelines saepius cornei, majores usque ad 2,5 cm longi centrales solitrarii interdum uno alterove aucti. Flores ad..."
My photocopy blurs badly at this point so I cannot complete copying this with any accuracy.
I lack enough data to know anything definitely other than this is a mess and there seems to be no meaningful way to untangle this gordonian knot without a sharp knife.
The ONLY reason this description has any value is due to it discussing a plant that was readily locatable due to being under cultivation. If it had been in reference to a wild plant no one could have found it again.
It is actually funny that macrogonus served as the type for the genus Trichocereus. Or that this could be respected and grandfathered into acceptance by any later workers.]