Bivalvia, commonly known as bivalve mollusks, are a class of mollusks that includes clams, mussels, oysters, and scallops. They are characterized by having a two-part hinged shell that is bilaterally symmetrical. Bivalves have a unique dentition, which refers to the arrangement and types of teeth or tooth-like structures in their shells.

Let's examine each option given in the question and the corresponding type of dentition and representative genus:

a) Taxodont - Nucula:
- Taxodont dentition refers to a series of small, similar-sized teeth arranged in a single row along the hinge line of the shell.
- Nucula is a genus of bivalve mollusks that exhibits taxodont dentition. The teeth in Nucula shells are numerous and uniform in size, forming a continuous row along the hinge line.

b) Isodont - Spondylus:
- Isodont dentition refers to teeth of varying sizes and shapes, with some teeth being larger and more prominent than others.
- Spondylus is a genus of bivalve mollusks that exhibits isodont dentition. The teeth in Spondylus shells are irregularly spaced, with some teeth being larger and more prominent.

c) Pachydont - Hippurites:
- Pachydont dentition refers to thick and heavy teeth that are well-developed for grinding and crushing food.
- Hippurites is a genus of bivalve mollusks that exhibits pachydont dentition. The teeth in Hippurites shells are thick and strong, adapted for crushing and grinding.

d) Desmodont - Mya:
- Desmodont dentition refers to teeth that are fused together, forming a continuous plate-like structure.
- Mya is a genus of bivalve mollusks that exhibits desmodont dentition. The teeth in Mya shells are fused together, forming a plate-like structure that is used for sifting and filtering food particles.

Therefore, the correct combination of type of dentition of Bivalvia and the corresponding representative genus is:
a) Taxodont - Nucula
b) Isodont - Spondylus
c) Pachydont - Hippurites
d) Desmodont - Mya

These combinations represent the different types of dentition found in bivalve mollusks and their corresponding representative genera.