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Photo#123189
Marsh Beetle - Prionocyphon discoideus - male

Marsh Beetle - Prionocyphon discoideus - Male
Groton, Middlesex County, Massachusetts, USA
June 28, 2007
Came to the porch light.

Moved

Prionocyphon
While using the Water Beetles of South Carolina (Ciegler, 2003) to ID another Prionocyphon, I notice she uses antennal color to separate the two. With that, these with all yellow antennae are P. discoideus. P. limbatus has antennomeres 4-11 dark/piceus.

Moved
Moved from Prionocyphon.
I consider it safe to move it here. Long antennae indicate male sex, and the contrast in colour of antennal segments 3 to 4 is distinct. The typical limbata in BG has the center part of the antennae black, getting lighter again to tip. Maybe this is a specimen not fully coloured yet, or a light variant.

Thanks Don
Moved from Marsh Beetles.

Prionocyphon sp.
Only two species, and it is identifiable to species from the photo if a key is in hand.

 
D&A key
the Downie and Arnett key uses the prosternum, except if it's a male. Male P. discolideus have "biappendiculate" antenomeres 4-10, whereas P. limbata have simple. However, the description of P. limbata indicates the "anetenna black or piceous with 3 basal antennomers yellow" and doesn't mention anything about a large black elytra spot. I couldn't find any web images of P. limbata, but is that enough to call this one P. discolideus?

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