The Beginning of the End of the Secret Mark Conspiracy Theory

 Clement of Alexandria clearly did write the Letter to Theodore because Morton Smith did not know Fragment 4 of the Hypotyposeis nor ever references it where the death of St Mark at Alexandria is specifically referenced:

op. cit. I p. 201. In Cod. Marcianus lat. 21, 10 (13th century), according to J. Valentinelli, Bibl. ms. ad S. Marci Venetiarum, Codd. Lat. Tom. V (Venice 1872) p. 214, there stands—after Peter Comestor’s Historia scholastica—in another hand a list of the burial places of the apostles, in which Clement of Alexandria is cited at the end. Zahn therefore had it printed as Fragment 12 of the Hypotyposeis. The same list, with identical wording, is also found in Cod. Paris lat. 9562 (12th–13th century), fol. 142v, discussed by R. A. Lipsius, op. cit. I p. 214f and Supplement fascicle p. 17. The list reads, according to Valentinelli, Lipsius, and Schermann (Propheten- und Apostellegenden p. 296; Prophetarum vitae fabulosae p. 213), as follows (P = Paris, M = Marcianus): 

‘Peter and Paul are buried at Rome. Andrew [is buried] at Patrae, a city of Achaia. James of Zebedee [is buried] in the citadel of Marmarica. John [is buried] at Ephesus. Philip with his daughters [is buried] at Hierapolis of Asia. Bartholomew [is buried] at Albone, a city of Greater Armenia. Thomas [is buried] at Calamia, a city of India. Matthew [is buried] in the mountains of the Parthians. Mark [is buried] at Alexandria in the Bucolis. James of Alphaeus [is buried] beside the temple. Thaddaeus and Judas [are buried] at Berytus of the Edessenes. Simon Cleophas, who is also called Judas—after James bishop for 120 years—was crucified at Jerusalem by order of Trajan. Titus [is buried] in Crete. Crescens [is buried] in Gaul.’ [Then comes:] “The eunuch of Queen Candace, one of the Seventy apostles, [was] in Arabia, which is called ‘Happy’ [Arabia]; he suffered [martyrdom], as Clement says in the fifth book of the Hypotyposeis, that is, of the ‘Instructions’.”

Morton Smith on the claim that Mark came to Alexandria, see Clement of Alexandria and a Secret Gospel of Mark p 27:

The tradition that Mark came to Alexandria does not appear in the preserved works of Clement of Alexandria, but Clement and Papias were probably the sources from which it was drawn by Eusebius of Caesarea (HE II.16). The φασίν that now stands in the first sentence of II.16, if not used impersonally, should refer to Clement and Papias, who were named as the sources of information in the preceding sentence. [C.M. considers this suggestion concerning the subject of φασίν plausible. J.M., however, argued that because “we have no tradition … about Mark’s connection with Alexandria before Eusebius (HE II.16),” this letter therefore depends on Eusebius.]