Mammillaria maritima
It is rarely grown in the collections even if it was discovered 50 years ago.
 

Description: Clumping cactus, irregularly  forming clusters up to 1 m across or more.
Stems: 20 to 50 cm long, 7 cm in diameter, cylindrical, narrow, eventually clumping near the base of the plant, somewhat jointed, initially erect then procumbent sometimes trailing and densely spiny. Glaucous-green then grey and corky in age but often reddish if grown in full light,
Tubercles: Conical or slightly flattened laterally, woolly when young.
Areoles: At first bearing grey wool then naked.
Radial spines: 10 to15, reddish brown, acicular up to 12 mm long.
Central spines: 4 reddish brown the upper three ascending, spreading, 1-2 cm long, straight. The lowermost stronger, longer and hooked 3 – 5 cm long.
Roots: Fibrous or moderately thickened.
Flowers: Produced near the plants tip from axils of tubercles , long, scarlet, 3-4 cm long, 2 cm wide. zygomorphic with a long hypanthium, segment flaring and tips reflexed, style as twice as corolla, stamens exerted half as far as style, filaments and anthers red.
Blooming season: March - April.
Fruits: Red, obovoid or globose.
Seeds: 0,5 mm long, black minutely pitted.
Remarks: Cochemiea pondii has thinner and several hooked spines per areole while Cochemiea maritima has usually only one hooked spine per areole.
 

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Scientific name:  Cochemiea maritima G. E Lindsay
Published In: Cactus and Succulent Journal 8(9): 144, f. s.n. (p. 144). 1937. (Cact. Succ. J. (Los Angeles))

Origin:  Mexico: endemic to Pacific coast of the peninsula Baja California (Approx from Punta blanca to punta rosalia, west of Punta prieta)

Habitat:   Grows in non calcareous rocks on slopes and rocky marine cliffs.

Conservation status: Listed in CITES appendix 2.

Synonyms:  

• Cochemiea maritima Shurly
  In: Cact. Jour. [British] 4:12, 1935. Nomen nudum.
• Mammillaria maritima (G.E. Linds.) D. R. Hunt 1971
• Mammillaria pondii ssp. maritima (G.E. Linds.) D.R. Hunt
  In: Mammillaria Postscripts 6: 5. 1997.

Cultivation: This plant isn't famous for being easy to cultivate, but in good conditions with excellent ventilation, it grows without difficulty.  It is especially sensitive to over-watering. So careful watering and an open mineral potting soil are a must. Avoid the use of peat or other humus sources in the potting mixture.
Don't add limestone to the potting mix, which must be moderately acidic.  Can be sensitive to frost.  Requires maximum sun exposure to reach its full potential. and in order to achieve success in flowering.
A winter rest that allows the plant to shrivel will encourage flowering and long term survival.  Be careful to encourage slow growth.

Propagation: Seeds or offsets.