135 

 THE SHELLS OF THE HOLDERNESS 

 BASEMENT CLAYS. 



ALFRED BELL. 



{Continued from page 59). 



Asiarie banksii Leach is often used instead of A. compressa 

 Mont. The latter name is so well known that for present 

 purposes it is not worth changing, and has so many varieties 

 of which the A. warhami may be an extreme form. A. 

 banksii is here used for the elongate type and A. compressa 

 for the more circular varieties. 



A. compressa latior is probably one of Bean's M.S. names. 

 It is quoted in Forbes Memoir (Geol. Surv., Vol. I., 1846, p. 414) 

 as var. B. [latior) now essentially northern, and by Prof. King, 

 Ann. Nat. Hist. XVIII., as a Bridlington Shell. A specimen 

 in the York Museum is nearly one inch broad. 



A. compressa nana, a small shell in the York Museum, 

 labelled A. indefinita in Bean's well-known writing seems to be 

 the A. compressa var. nana Jeff., B.C. ii., p. 316. 



A. richardsoni, figured in Belcher's Last of the Arctic 

 Voyages, pi. 33, fig. 7 (1855), is a well-grown shell, L. 30 mm. 

 B. 38 mm. It is rare in Bridlington. 



A. placenta Morch is well figured by Jensen, Danish Ingolf. 

 Expedition, 1912, pi. IV., f. c d, and by Leche, Svenska, Exped. 

 till Novaja Semlja in 1878, pi. I., fig. 4. 



A fine shell in the York Coll., labelled A. fluctitosa in Bean's 

 writing appears to be a very elongated form of A. semisulcata, 

 H..24 mm., B. 45 mm., apex nearly central. It seems to be 

 an extreme example of the var. sericea Posselt. (Med. om. 

 Green., XIX., pi. I., fig. 8-12, and by Jensen op. cit., pi. IX., fig. 

 1 /. The above three shells appear to belong to the semisulcata 

 group, frequently known as A. borealis. 



A. elliptica (crassa Leche) Brown. The Bridlington shell I 

 refer to this is figured by Jensen, op. cit., pi. IV., fig. 40, as 

 A. elliptica var. crassa Leche, pi. I., fig. $ab. It has little 

 reference to the shell we consider as the type. 



The A. lactea of Brod. and Sow., figured by Dautzenberg and 

 Fischer in the Monaco Scientific Expedition (Mollusques), pi. 

 XL, figs. 26 to 28, seems to be the same as that figured by 

 Wood, Crag Mollusca, pt. 2, pi. XVL, fig. 3, as A. withami. 



Note D. — Acila — The shells of this ornamental group of 

 Nuculas abound in the Bridlington series, frequently in pairs, 

 but more often in various sized fragments. Small valves 

 from barely 3 mm. in diam. upwards are present. 



The name shell A. cobboldice J. Sowerby, is very variable 

 in the later pliocene series, ranging from a nearly circular to 

 the angular types figured by Mr. Wood — or probably there 



1917 April 1. 



