ABSTRACT
The shell consists of a single piece, generally without any suture, even on the internal surface; and this is the case, at least in Pyrgoma Anglicum, in extremely young colourless specimens. The scuta and terga are calcified together, without any trace of a suture; the line of junction can be inferred only from the analogy of Pyrgoma conjugatum, in which species the valves have a more normal character, and are separated by a slight furrow. The present species, with the last two, form an interesting series. Pyrgoma grande and conjugatum, however, are more closely allied to each other than to Pyrgoma cancellatum. Animal's body from some cause, perhaps from the corals in which the species of Pyrgoma are embedded, long remaining damp, the internal organs is generally badly preserved. In the scutum, the whole valve is least elongated, with the adductor plate least developed, in Pyrgoma grande, and most elongated, with the adductor plate most developed, in Pyrgoma cancellatum.
