In 1900, the idea of the pecten came from a man by the name of Mr. Grahm. Mr. Grahm was once the director of The Shell Transport and Trading Company. The shell was an emblem taken from his family coat of arms. It originally began as a realistic rendering of a pecten in black and white in 1900. And by 1930, the pecten was an upright standing shell with graphic details. Color was not introduced until 1948.
The icon that we see everywhere today was created by Raymond Loewy, who also created logos for BP and Exxon. Although Loewy created such iconic logos, he was predominantly an industrial designer. His revision came about in 1971 and is still the foundation of the logo we see today. Loewy was born in France and was one of the best known industrial designers in the 20th century. He contributed to the branding of Greyhound bus, the Pennsylvania Railroad and locomotives, and Lucky Strike. Loewy also contributed to the refinement of Coca Cola packaging. He transformed the "Mae West" bottle into a silhouette that was sleeker and sexier to the new generation. His career and influence were present in the industry for seventy years, he then retired to France where he passed at the age of 93 in 1986.
There have been a couple different versions since 1971, but it is essentially the same logo. The logo has very distinct yellow and red colors which is equally important to the identity as the form itself. These colors were chosen because of their striking qualities, but also because they are the colors of Spain. This is significant because the company was California based and many early Californian settlers were born in Spain. Today we don't even need the name of the company to recognize that this logo is the identity of the Shell company.
For curiosity purposes, here's the link to Raymond Loewy's website: