Hi, sorry to be years late, I just discovered this image. The male spider's left palp (white arrow) appears to have the embolus thick and heavy and the tip is broken off. This is injury is not that unusual in spiders and sometimes the broken end is found in the epigynal opening of a female! From the thickness of the bit of the embolus we can see, and based on the dorsal appearance of the cephalothorax, I do think this is A. pennsylvanica. The coloration is a bit pale, so I had a good squint at this one. Most pennsylvanica are darker and browner, the pale/ochre/olive ones are sometimes A. utahana, or kastoni hence my squint.

The bulb of what looks like liquid appears to be the edge of the inflated hematodocha of the right palp (which is itself largely invisible behind the body of the female). The hematodocha is an inflatable pouch that fills with hemolymph (blood) and acts to squeeze the semen out of the palp into the female. It alternately inflates/deflates during mating. It is NOT filled with semen (which might seem logical to the naive viewer). Of course the view is not very clear, so I may be wrong about this. If it is indeed a droplet of semen something has gone seriously wrong for this couple, it should never be out in the open.

Moved from Grass Spiders.

Moved from Spiders.

Moved from ID Request.

The bubble is probably sperm. A male spider uses his palps like a syringe. They produce a drop of sperm, suck it up with their palps and then use them to deposit it into the female. This could very well be A. pennsylvanica but the species in this genus are very hard to distinguish without a clear shot of the genitalia. I'll let someone else decide whether it should be placed at genus or species.

please correct the County field