348 ME. E. S. COBBOLD OIN' THE [vol. lxxvi, 



Localityand horizon . — C omley , Middle C ambrian ; from the 

 Billingsella Beds, horizon Be. 



Aceotbeta sp. indet. b. (PL XXIII, fig. 30.) 



A few valves were found in fine blue shale in the bed of C omley 

 Brook; all are much crushed. Fig. 30 [1606] represents one of the 

 best-preserved ventral valves. 



Dimensions. — Length =1*2 mm. ; width = 1*4 mm. ; height, 

 greater than "4 mm. 



Locality and horizon. — Comley, Middle Cambrian ; horizon 

 Ba 2 . 



Acroteeta sp. indet. c. (PL XXII, fig. 34.) 



Two dorsal valves [1621 a, 1622] that appear to belong to the 

 genus were found in sandy shale east of Hill-House Badge. 



The internal characters are well marked, but there is not sufficient 

 material for specific determination. 



Dimensions in millimetres. 

 1621a. Lengths 2'4, width=2'5. 

 1622. Length = 1-5, width= 1-7. 



Locality and horizon. — Comley, Middle Cambrian; horizon 

 Bb,. ■ 



Aceothyea Matthew. 



Dr. Gr. P. Matthew x proposed the generic name Acrotliyra for 

 certain Acrotreta-lUke forms having 



' the ventral valve elongate-conical, with the apex either overhanging the 

 cardinal line, or but little in front of it ; [and the interior] with a long, 

 narrow, or a quadrate visceral callus, extending forward from the foramen 

 about a third of the length of the valve and widening as it goes.' 



Dr. C. D. Walcott, 3 in his monograph, adopts the separate generic 

 term ; but he observes that 



' this genus is intimately related to Acrotreta, and, except for the presence 

 in some species of a well-marked visceral area of a type not known in Acrotreta, 

 there would be difficulty in assigning more than subgeneric value to it.' 



The Comley specimens that are here assigned to Matthew's genus 

 are very like Acrotreta ; but they have a strongly-marked visceral 

 area in the ventral valve, and in the dorsal valves the main vascular 

 sinuses are well developed. 



ACEOTHYEA COMLEYENSIS, Sp. 110V. (PL XXIII, figs. 1 a— 8 ; 



text-fig. 3, p. 349.) 



Acrothyra sp., Cobbold, 1916, Rep. Brit. Assoc. (Manchester, 1915) p. 119. 



Type-specimen [1710]. 



Diagnosis. — Ventral valve subcircular. conical; apex pointed, 

 and somewhat in advance of the posterior margin ; false area ill- 

 defined, traversed by a broad vertical channel and inclined forwards 



1 Bull. Nat. Hist. New Brunswick, vol. iv (1901) pt. 4, No. 19, p. 303. 



2 1912, U.S. Geol. Surv. Monogr. vol. li, p. 716. 



