ID help needed from Mexico

[MICHAEL ZARTUN]

was found in the northern most region of the Sea of Cortez, Puerto Peñasco, Mx. Just shy of 6" X 2", and it's a broken pc. Appears to be all Mother of Pearl. Four lobes, for a lack of a better word bound by what appears to be the same ligament tissue that binds bivalves. It was flexible somewhat when wet, now not at all. It kind of reminds me of the internal closing 4 lobes of a barnacle on a grand scale. Ideas?????

[paul monfils]

This is the anterior end of a pen shell, family Pinnidae. It doesn't actually have four lobes. It has two valves, but each of them in this specimen is broken down the middle. These large shells are extremely fragile, and have a very thin outer layer, which is completely eroded away in this specimen, exposing the somewhat thicker pearly inner layer. There is no way of identifying the exact species from such a small and eroded specimen, but since it is from the Sea of Cortez there are five possibilities - Pinna rugosa, Atrina maura, Atrina tuberculosa, Atrina oldroydii, and Atrina texta.

[MICHAEL ZARTUN]

Paul---Muchas Gracias, for your prompt and informative reply. Will do some research with your info, real curious abt the the whole creature. Thanx again