This female Hylaeus has a very elongated head (CI=1.74 !!) and does not fit within the range of any described species. It belongs to the Prosopis subgenus. I think it’s H. gibbus with some doubts with H. pictus and H. garrulus.
Drowned in a pool, 18.viii.2017. [Iberian Peninsula: Catalonia: Girona: Beuda: 380 m a.s.l.]. Sex: female (12 antennal segments). Length: 6.25 mm (but could be more as gaster got a bit telecopied inside) . KI, Kaput Index (length head/width head): 1.07. Interocular index (distance between internal orbits at vertex/ distance between internal orbits at malar area): 1.40. CI, Clypeal index (length clypeus/ width clypeus): 1.74!!.
HEAD: Mandibles with two teeth. Clypeus slightly convex, without projections or teeth. Clypeus partly stained with red-brown. Vertex flat: in frontal view, the upper edge of the head is clearly above the upper orbits only in the middle and with a height less than the composed eye width. Internal orbits converging downwards. Head trapeziform, not rectangular. Occipital keel present. Facial foveae reaching the upper part of the orbits, the highest point nearest to the orbits than to the ocelli, and both foveae converging only a bit between them. Malar space long (=4/40 mm), almost half of its distal width (=10/40 mm). Seen laterally, temples narrower than composed eyes.
THORAX: Pronotum pale with convergent sides and blunt, not squared angles. Thorax black, without red colour. Seen laterally, mesopleuron rounded anteriorly. The punctures at mesopleuron are bigger than that of first tergite. Lateral and terminal areas of propodeum finely sculpted and felted. Medial area of propodeum rugose. The edges between lateral and pleural areas and between lateral and terminal area are rounded, blunt. Only the terminal area of propodeum in contact with pleural area is sharply laterally flanged. Scutellum black.
GASTER: Black. Tergite 1 (T1) with haired apical bands. Tergite 1 finely punctured, the base sparsely punctured, and with some transversal striation. The terminal edges of tergites are just a bit more pale, brown coloured. Sternite 6 has some thick deep brown hairs.
LEGS: Basitarsi of all legs black.
I’m quite sure about the Prosopis subgenus. I think it’s gibbus with some doubts with pictus and garrulus. The head is very elongated in this specimen and does not fit within the range of any described species.