Agkistrodon howardgloydi is a species of venomous snake, a pit viper in the subfamily Crotalinae of the family Viperidae.

It is a rare species with a relatively small geographic distribution in the tropical dry forest on the Pacific coast of Honduras, Nicaragua, and extreme northwest Costa Rica.

[4]: 91 p. [7]: 249–265 p.  No clinical reports on envenomation had been published (as of 1999), but laboratory texts and analysis indicate the venom is highly toxic and similar to its close relative Agkistrodon bilineatus, and potentially lethal.

[8]: 482 p. Roger Conant's original description states: "This subspecies is named for the late Howard K. Gloyd, my close friend, colleague, and expert on pit vipers, especially the rattlesnakes.

Gloyd worked for decades on the genus Agkistrodon (sensu lato), and he had predicted that a new race of A. bilineatus would eventually be described from lower Central America.

The bottom side of the head, chin and throat area, is orange or orange-brown and distinctly lighter than the ventral scales which abruptly turn darker on the neck and body.

[11]: 622 p.  The type locality given is "0.8 km north Mirador el Cañon del Tigre, Parque Nacional Santa Rosa, Provincia Guanacaste, Costa Rica".

[4]: 93 p.  A study conducted early in the rainy season of 1994 in Costa Rica found some age related variation in the diet: neonates (<38 cm.)

Likewise, vibora castellana is another name used for both Agkistrodon bilineatus and A. howardgloydi on the Pacific coast of Guatemala to Costa Rica.